Why are modal verbs in English defective?

Question: Modal verbs exist in many languages; but they are often defective. English is an extreme example where they seem to only have present tense forms; and have no gerund, participle, or infinitive; some also lack a past tense. I was wondering how does that happen? I know that other Germanic languages have modal verbs that are less defective than those in English; for example, the German "kann" has a past tense and an infinitive; unlike its English cognate "can". Did those verbs ever have some of the missing forms in modern English centuries ago? If so what were those forms? Or are some of the forms missing in English but present in German innovations of German?
Comment: See also this question and its answers: https://linguistics.stackexchange.com/q/17324/9781
Comment: @S.G. Yes, *can* is suboptimal for several reasons; its periphrastic tense-bearing version *be able to* necessarily resists *can*: ❌ *You can't be able to say this* just like ❌ *I will be going to do that soon.*  //  *Must* doesn't have an analytic past tense, but it sure feels like it has a synthetic one of sorts: *That must be John* > *That must have been John*. It seems to work out ok, even if you don't have the same flexibility as you have with *will*: *That will be John* > *That would be John* analytically vs.  > *That will have been John* synthetically.
Comment: @S.G.: If you're going to accept the periphrastic "to be able to" as the infinitive of "can", why not say that "to be required to" is the infinitive of "must"?
Comment: I believe "can" is a suboptimal example; its (irregular) past tense is "could" and its infinitive in use is arguably "to be able to" (which is clearly highly irregular and compound). "Must" may be a better example as it lacks a past tense entirely and it has no infinitive in common usage.
Comment: excellent point, @S. G
Answer: The simple answer is that they cease to be "verbs" and become some other category entirely. In the formal study of syntax, we could say they have category T ("tense") instead of category V ("verb"), or more simply we could say that they're now "modals" rather than "verbs". The purpose of these labels is to talk about shared behaviors, after all, and modals and verbs don't behave very similarly at all.
As for how this change happens, syntactic reanalysis and specifically grammaticalization is a common way for languages to change over time. Those terms should lead you to good resources on it.
In many cases, both the present and past forms of English modals are still around: can~could, will~would, shall~should, may~might. (The big exception is "must"; "mote" has died out except in a couple fossilized phrases.) We still see this alternation when the "present" modals are used in a past context: "I think he will do this" but "I thought he would do this".
Other forms have died out, but can be seen in older varieties of English, when they still conjugated like verbs: "canst" (second person singular of "can") and its ilk appear in Shakespeare, for example. They generally look exactly like you'd expect (predictable endings stuck onto the verb stem). A few have taken on a life of their own, like "cunning" (originally a participle from "can"), and are now used without any apparent connection to the verbs that birthed them.
Comment: @Draconis: The *give* in *can give* is an infinitive (without *to*, but still), to be a finite form it should display person, number, and tense which it doesn't.
Comment: I think this answer should either explain what T and V mean or to link to an explanation of them. I don't think these terms are generally understood.
Comment: It's the modals' lack of infinitive forms like **to shall* that gives rise to the prohibition against double modals in standard written English.
Comment: "Mote" died out, but was replaced with the periphrastic "had to."
Comment: In modern English, the infinitive is the simple uninflected form of the verb: *be, come, go, have*. Additional particles (*to VB*) or complementizers (*for NP to VB*) are variously **required, forbidden, *or* optional** depending on construction, syntactic role, and verb class: *he must go, he needn't go, we made him go, we let him go, we helped him go, we saw him go, we went to see him, we asked him to go, for him to go was unexpected.* In general, modal verbs, causative verbs, sense verbs, and a few select catenative verbs require bare infinitives which brook no particle in modern English.
Comment: not verbs; but some type of gramatical particle; that was my gut analysis of modals, but i kept reading that linguists regard them as verbs so I am no longer sure of that
Comment: @Araucaria-him The big one is that they can't receive tense or agreement features. But "do", at least in Adger's model, can get inserted at T, so apart from the features it does fulfill the same role syntactically.
Comment: @Draconis: I see.  I hadn't heard that expression before.  A bit of Googling shows that it's a Freemason ritual phrase, later borrowed by Wiccans and Pagans.
Comment: @tchrist Is it? Modals are usually followed by finite forms: "can give", not *"can to give".
Comment: Apart from the fact that they are defective, how do modal verbs differ, for example, from the auxiliary verb *do*? They seem to behave in pretty much the same way to me!
Comment: @Draconis Well, yes, maybe, but not receiving tense or agreement features *is* being defective. And how can they be category T if they have no T? Main point: It can be argued they *do* in fact behave like other verbs to varying extents, to a great extent when it comes to auxiliary *DO*!
Comment: What are the "couple fossilized phrases" that still use "mote" as a modal verb?
Comment: @dan04 "So mote it be" is the main one.
Answer: This is the result of historical devolopment.
The Germanic language (all of them) have a bunch of verbs where the past tense acquired a present tense meaning, called Präteritopräsentia in the German literature. This class of verbs was originally not restricted to modal verbs, the German verb wissen "to know" is a member of it, and the English verb to dare also belonged to it (You can still say He daren't do this without third-person s on dare). The verb will was originally not a member of this class but in a class of its own even going back to Protoindogermanic (compare the irregular Latin verb velle).
Now, in English the only surviving verbs of this class are all modals, and almost all modals belong to this class, with the exception of will that was later assimilated into this class. While German completed the conjugation paradigm for its präteritopresentia, the English ones stayed defective in some sense (no participles, no future tense, and the past tense can easily be reanalysed as just another verb with specialised meaning).
Comment: Cognate to German *wissen*, the now-archaic English verb [*to wit* is also a preterite-present verb](https://www.oed.com/view/Entry/229569), with present-tense inflections like *I/he wot, thou wost*. Like all verbs of its class, it underwent a great deal of conjugational confusion and reänalysis over time, leaving only a few fossil vestiges in today's language. // For modal *dare*, see also *durstn't* in the past tense.
Comment: Maybe, I don't have the details, specially about older stages of English, ready. I just wanted to illustrate the different routes of development of them in English and German.
Answer: The lack of non-finite forms for English modal verbs seems to be associated with their role in English grammar as a special kind of auxiliary verbs.
These verbs share the historical morphological property of being what are called "preterite-present" Germanic verbs. There are attested non-finite forms, including infinitives, for some preterite-present verbs. But it seems like the absence of non-finite forms was an early characteristic feature of those preterite-present verbs that were used as modals.
According to the paper "The evolution of surviving English preterite-present verbs (āgan, cunnan, *durran, *magan, *mōtan, *sculan): a corpus-based study" by Magdalena Tomaszewska, several of the ancestors of English modal verbs such as *mōtan and *sculan (the ancestors of modern English must and shall/should) are already unattested in the infinitive form in Old English (Table 1, page 3). (A previous version of this answer incorrectly stated that they were attested—I was confused by the practice in dictionaries of citing these verbs by their hypothetical infinitive.)
However, can was attested in its infinitive form cunnan. The explanation seems to be that can and other preterite presents that were used in the infinitive did not have a modal meaning when so used: for example, cunnan was also used to mean "to know" with a noun as its object.
Thus, "Grammaticalization of modals in Dutch: uncontingent change" (Griet Coupé and Ans van Kemenade, 2009, Chapter 15 in Historical Syntax and Linguistic Theory, editors Paola Crisma and Giuseppe Longobardi (eds) (2008) Oxford University Press) summarizes which forms are found in early Germanic languages as follows:

We conclude that Old Germanic preterite presents, when they have modal meaning and take an infinitival complement, are always finite. Thus, they cannot feature as the middle member of a three-verb cluster. (page 4)

The development of non-finite forms of modal verbs in some modern Germanic languages such as Dutch is described by Coupé and Van Kemenade as a later innovation (page 8).

As for why the grammaticalization of these verbs as modals goes along with them lacking non-finite forms, that I am not sure about.
Frans Plank, in "The Modals Story Retold" (1984) writes "the modals would belong to a word-class for which all these verbal paradigmatic categories as such are irrelevant in the first place, rendering the concepts of paradigmatic gaps and zero exponents strictly speaking meaningless" and suggests that they "have to be conceived of as finiteness markers of their clauses or verb phrases" (page 328).
Answer: Speaking of these modal verbs as defective is derived from the attempt of fitting everything nicely into square boxes. Deriving them from Proto-Indo-European is no small task not only because they do not fit nicely into these boxes. In some cases, the roots themselves are not entirely certain. To derive them from first principles is to work our way backwards, however.
Since "can" is in question, intuitively speaking, German kann ("can") could have a weak preterite in kannte ("knew"). "I knew to" has perfect semantics which could has not. Since subjunctive and past tense have merged, could is rather imperfect. German still distinguishes pret. konnte from Subjunctive könnte, but the latter is equally expressed by kann ja, könnte ja*, which could be a reanalyzed cognate from present subjunctive *-ī on the respective stem. The reconstructed root for can and know would be the same Proto-Indo-European *ǵneh₃- "to know" in some view, but the matter seems to be unresolved. can < *kunnaną < *ǵn̥-né-h₃-ti has an n-infix and a sylabified nasal, correctly reflected in u (cp. un- < *n-); know < *knēaną on the other hand is optimistically deemed cognate, "but the exact mode of derivation is unclear", "''apparently from *ǵneh₁-, of unknown origin''", without Gothic comparisons. (Wiktionary1, 2, 3).
This leaves room for idle speculation, which is on its own not reliable. Eg. zero-grade *ǵn̥h₁ is not unknown, cp. *kunją "kin, family", *knōsl "race, descent", see also Ger. Bekannte "friends", bekennen "confess" (be alied to). Though it is true that etmylogies for these roots are wanting, linguists seem to agree that they are not related, which brings us back to the question about modal verbs, although the laryngeals are not supported on the Germanic side.
The other ones are shall, will, must, may, † tharf for canonical examples, further, ought to, used to, dare (Wikipedia), and I dare add to try for good measure. Every single one of them is questionable.

shall / shoul < *skal (infinitive *skulaną) < PIE *skel-4 is per se not convincing, and Baltic cognates in close proximity to Germanic don't change that.

English has of course to scold. Related Ger. beschuldigen "to blame, implicate", Schuld "guilt, debt" < PIE *skél-ti-s ~ *skl̥-téy-s (Kroonen apud Wiktionary) is fairly important for legal history, making Schulz one of the most prominent names. However, the verbing may very well be backformation from the adjective, schuldig, Old High German sculdīg, inasmuch as participles cover both grounds. Pfeifer glosses "sculdīg `schuldend, verpflichtend, verpflichtet, zugehörig, geeignet' (8. Jh)"5, ie. obliged: cp. German part. obliegend, ind. auferlegen, aufschlagen. This pseudo legalized layer of Germanic by extension, is poorly understood because it would have been writen almost exusively in Latin if at all.
As far as the evidence goes, the word might just come from the confluence of several idioms, eg. weregeld" blood money": cp. gold, gulden, Geld, or better heilen" (judicial "to restitute"). Guilt is etymologically uncertain, mind. However, much more striking are the isoglosses gel, wa (ca. "isn't it?"), the former allegedly short for gilt es, akin to guilt, the later from wahr "true, very", possibly influenced by wad "what" (as in Singapor English), because Germanic w- seems to have been loaned as gu- into French, cp. guarantee, warantee, quarantine, and quid, Quittung, quod erat demonstrandum. Also of interest, cuckold, cockewald, -wald, in a conceivable legal sense "plaintiff" would point to a common root *(h₂)welh₁-, cp. Anwalt "lawyer", but the first element remains unknown since cuck is compared to the cuckoo call and judged sound-immitative, so that diminutival suffix -ulus wouldn't even seem that strange. Jt's a cold case, since sigmatic aorists have no place tbis side of the schizma.

will, would, want < ...

Incidently, *h₂welh₁- is reconstructed as the root of will. See my so far unanswered question for more (Origin of "will" in Germanic, wouldn't it be subjunctive?). More recently I argued that to want also belongs here. Again, mainstream communis opinio finds *h₂welh₁- and *wenH- unrelated. Oh Well! Even though, a subpletive paradigm may be gleaned.
It is fairly obvious in my humble opinion that may and must have been related. This must be difficult to workout because of several situational interpretations with as broad a meaning as "to go", to which cp. miktieren, Latin meō "go about, wander", moveo "move".
Besides the n-infix, productive negation as per wouldn't throws things out of proportion. mustn't and muss nicht are notorious false friends.
The root noun might on the other hand is chiefly nort-west European when triangulating the evidence (cf. JIES '22 Vol. 1). It would be wrong to reconstruct this for PIE.

The other ones wont fare much better, I'm affraid.


Blue smoke surrounding me in Dragon Age: Origins

Question: I just successfully defended Redcliffe in Dragon Age Origins as a Mage.  I noticed that there is some blue smoke surrounding me, but looking at my 'modifiers' the only thing I can see is 'coughing blood'.  Is the blue smoke a glitch or is there something which might cause it?
Comment: So it happened again.  I think it has something to do with casting a spell just as a battle ends.  The spell surrounds me in smoke for a second, but if battle ends, the animation sequence gets interrupted.  It disappears next time you transition.
Answer: "Blue smoke" sounds like the spell cleansing aura.  Check your mages to see if any of them have it active.
As mentioned in another answer, they likely cast the spell because someone in the party was injured.  However, my experience is that only the initial casting of the spell removes injuries, not the persistent "aura" effect which heals hit points.  So if you see the aura and are still injured, you need to turn off the aura, wait for the cooldown, then cast it again with your injured party member in range in order for it to remove the injury.
Answer: Blue smoke as in you have a spell active? Can you post a screen shot? If you're coughing blood use a injury kit to heal yourself and see if the smoke goes away.
IIRC when you have certain spells active they aren't listed as under the modifiers as that's only for something that is physically affecting you i.e ice enabled, that should list there, but other spells, say spell might iirc won't.
Comment: I think I may have had Frost Weapons (or whatever it is) enabled.  In any case, when I started playing the next time it was gone.  I didn't think to take a screen shot at a time :-p
Answer: Coughing blood is a modifier caused by an injury so it should not be related to the blue smoke. Apply a heal kit to your party member who has the coughing blood modifier and that should cure it.
It sounds like a Spirit Healer (mage) who is casting cleansing aura, however be aware that Cleansing Aura will not remove an injury on the Spirit Healer themself

While this mode is active, waves of healing and cleansing energy emanate from the caster, restoring health to all nearby allies every few seconds and curing the injuries of allies very close to the caster.

For more information on injuries such as coughing blood, click here
Comment: Ah.  I'm not a spirit healer, but I do have one in my party
Comment: I bet they are auto casting it because of the injury
Answer: Note that if you use a lesser injury kit instead of a normal one it will get rid of other injuries so you might want to use more than one or use a greater injury kit unless he/she only has one injury. And it might take a while before you have cleanse aura.
Answer: it is a bug that happens when a specific sustained talent(I don't remember the name of the sustained talent) remains active after a cut scene occurs at the end of the battle. Just save , exit game and load, that solved my problem
Answer: You have two different problems:

The blue smoke: fix using a templar's ability to Cleanse Area to make the smoke disappear (this will also cancel any other sustained mage abilities)
Coughing blood: use an injury kit.


What is the best source to study Classical Mechanics for a Grad Physics student who struggles to solve problems?

Question: I am a physics major student who graduated last summer. During my undergrad years and now in my graduate level studies I always worked experimentally. I worked in labs with professors for years. Of course with a moderate amount of studying and with the help of my succesful research career in experimantal optics, I graduated and accepted to the graduate school. I applied for research assistantship and took the exam. Unfortunately I realised that my knowledge and problem solving abilities had become dull over the years. Especially in Classical Mechanics. Could you suggest a book or two for a graduated student who took calculus and a intro. classical mechanics etc. what I mean is I know most of the concepts I don't need to start from the very bottom. I can understand derivations. What I need is a lot of solved examples and exercises with increased difficulty. I know I can't solve a tough problem on my own right now. I just need a guidance. Is there any source that can help me?
Answer: It sounds like A Guide to Physics Problems, Part I and Part II are precisely what you're looking for.  These two books are compilations of problems and complete, worked solutions from the graduate qualifying exams of some of the best universities in the world. Part I contains the mechanics, electromagnetism, and relativity sections, while part two goes into statistical mechanics / thermodynamics and quantum mechanics.
The problem range in difficulty from cute and mildly tricky to genuinely very difficult, but they are all unique and interesting.  Typically they do not require a lot of sophisticated mathematics - instead, the primary hurdles are conceptual (though of course, being qual programs, there is often no shortage of algebra).
Comment: Oh those look really interesting. I'll check them out. Thanks!


How can we tell whether a double beta decay is neutrinoless or not?

Question: If a double beta decay is neutrinoless, there will be no neutrino carrying the energy away and the electrons should carry the exact amount of energy of the decay. The problem is that because neutrinos are emitted in a continuous spectrum and neutrino masses are extremely small, it's difficult (if not impossible) to rule out the possibility that two near-zero energy neutrinos are emitted. In single beta decay there is no such ambiguity as neutrinos carry a half integer spin, which means the angular momentum won't be conserved without it. But in a double beta decay the angular momentum of two neutrinos can cancel out.
Comment: I'm guessing the idea is to compare the spectrums of emitted electrons, having massive neutrinos in the output means the endpoint of the spectrum is shaped differently due to the neutrinos possibly being at rest when emitted.
Comment: https://www.frontiersin.org/articles/10.3389/fphy.2021.666591/full  "Recording such an event would demonstrate that the lepton number conservation is violated by two units, but cannot indicate the mechanism that dominates this process. "
Answer: By using a detector with excellent energy resolution.

The problem is that because neutrinos are emitted in a continuous
spectrum and neutrino masses are extremely small, it's difficult (if
not impossible) to rule out the possibility that two near-zero energy
neutrinos are emitted.

The "difficult" bit is correct, the "impossible" bit is not. Many experimental collaborations search for neutrinoless double beta decay. One example is the GERDA experiment (now continuing as LEGEND). From one of their results papers comes this plot:

Shown in grey is the measured background after a lot of clever experimental work. Blue is the spectrum that is attributed to the two-neutrino double-beta decay, in this case of Germanium-76. Also indicated as $Q_{\beta\beta}$ and in red is the total energy of the decay. This is where you would expect the signal from neutrinoless double-beta decay to show up. For scale, note the gamma lines from radioactive Potassium ${40}$K and ${42}$K. These give you an idea of the excellent energy resolution of these detectors. Thus, given the statistics of this run, you do not expect any background from the two-neutrino decay in the region of interest to the neutrinoless decay. Had they seen a peak around $Q_{\beta\beta}$ it could not have been from the two-neutrino decay.
Note though that this feature is not a requirement. Other detectors have worse energy resolution but other advantages. Even if the two-neutrino decay leaks into your signal region, you can still fit its shape and subtract it from your measured spectrum. Though in that case indeed you do loose the possibility to distinguish the two decays on an event-by-event basis.
Comment: I don't see this. It's the same situation in double electron capture really, in the neutrinoless case, neutrinos are virtual, so they don't need to generate separate photons, but there's then simply a little bit more energy left in the total visible decay energy. So it's the same: you need excellent energy resolution. For phase space reasons (i.e. practical decay rate) though, beta decay is easier to search for the two-neutrino/neutrinoless distinction than double electron capture. See e.g. [this paper](https://arxiv.org/abs/2002.04239) for prospects using double electron processes..
Comment: What about double electron capture where all energy is carried away by neutrinos? If the two neutrinos annihilate, the energy has to go somewhere and become photons, which may be more easy to distinguish.
Answer: There are at least two main ways it can be done (of course, nothing prevents you from using both of them and using them as cross-checks on each other).
Measure The Electrons Only And Look For Missing Energy And Momentum
The way that neutrinos were discovered in the first place and the more comprehensive method is to look for them indirectly by looking at the electrons in the decays and to see if they can account for 100% of the energy in the system under conservation of energy and momentum principles.
Even though neutrinos don't have much rest mass, on average, they account for a share of the total energy of the decay products that was possible to detect with WWII era grade instrumentation and modern detectors are much better.
In double neutrinoless beta decay you have zero apparent missing energy which shows up in the kinetic energy and trajectories of the double emitted electrons, when in ordinary double beta decays, you should have an (on average) not terribly difficult to measure amount of missing energy in the electrons that fits a well defined distribution of momentum directions and magnitudes.
If you are willing to be model dependent, you know precisely how much energy a beta decay or a double beta decay should kick out, and so you just compare the energy you observe in decay products to the theoretical expectation in each case (with systemic uncertainties to reflect lack of 100% efficiency in your detectors after screening statistically for detector results that, for example, are obviously cases where there was a double decay but your detector only saw one electron).
Look For Neutrinos In Association With Electrons And Adjust For The Neutrinos Your Detector Misses Statistically And Background Noise
The other strategy is to put neutrino detectors in place. Now, since neutrinos have a very small cross section of interaction with almost everything, your neutrino detector isn't going to see every neutrino that actually decays. But, it is possible to determine to a fair degree of precision what percentage of neutrinos that pass through your neutrino detector are being detected. If you know how many neutrinos are being seen and your detector efficiency to reasonable accuracy, then you can place reasonable bounds on the total number of neutrinos being produced. (Ideally, you also adjust for neutrinos from sources other than the one you are measuring which create background noise which you can model and subtract out, and have a statistical elimination screen that excludes neutrino detections that happen without a corresponding election emission from your targeted source material.) You then compare that number to the number of neutrinos you would expect given the number of decays that occurred which you measured from an electron detector with a much higher efficiency since electrons have a much higher cross section of interaction because they have electromagnetic charge.
You then use the comparison to place statistical bounds on the maximum percentage of decays that could have been double neutrinoless beta decays, and analyze that statistically to determine if it is consistent with zero or not.
Adjust Statistically For Low Energy Neutrinos Emitted In Normal Double Beta Decay

The problem is that because neutrinos are emitted in a continuous
spectrum and neutrino masses are extremely small, it's difficult (if
not impossible) to rule out the possibility that two near-zero energy
neutrinos are emitted.

You can do a model dependent calculation of the share of neutrinos that will have near-zero energy and fall below your detection thresholds (in both methods). You can also cite to different kinds of experiments, theoretical calculations ab initio, and Monte Carlo simulations to corroborate the reasonableness of your assumptions in doing so and to place reasonable bounds on your systemic error from this part of the experimental setup.
Then, you adjust the neutrino detections or electron energy measurements that you actually do make in much the same way that you do for the overall efficiency of the detector.
All these adjustments can get pretty involved, but fortunately, radioactive decays are very well behaved and predictable at a statistical level, so you can lean pretty heavily on the parts of the Standard Model that you aren't actually testing in the experiment itself, without worrying about introducing significant theory error. This allows you to overcome a lot of unavoidable limitations of your instrumentation.
Model Dependent v. Model Independent Data Analysis
The most straightforward thing to do once you have your data would be to do a hypothesis test statistical analysis against the null of no double neutrinoless beta decay that is the Standard Model expectation.
This allows you to do things like dramatically reduce the systemic error, for example, by establishing predicted ratio of double neutrinoless beta decay to regular (neutrinoful?) double beta decay, which cancels out sources of systemic error shared by both kinds of double beta decay detections.
But, to do that you need to be doing a model dependent test and the problem with that is that since double neutrinoless beta decay is already beyond the Standard Model "new physics" there are a conceptually near infinite number of possible models that could produce neutrinoless double beta decay. So, if you only hypothesis test the most "vanilla" Majorana mass neutrino model you don't really know how robust your results are to subtle changes in the underlying theoretical model.
In contrast, without doing a hypothesis test, you can get a much more model independent bound on the results, but at the cost of not being able to cancel out a lot of potential sources of systemic error and not having a clear target that you are looking for that you can optimize your experimental setup to see. So you end up with results that just say "the neutrinoless double beta decay width is no more than X" without getting to zero, instead of the most satisfying but somewhat self-deceiving conclusion "we've [found] [ruled out] neutrinoless double beta decay at the five sigma level" (self-deceiving because it always comes with the footnote "if this thing that we've never seen actually works the way we think it does."
The glory of the five sigma exclusion instead goes to somebody who didn't put the blood, sweat and tears into doing the experiment who free rides on your experimental result and does a quick calculation of an expected value with what every model the cool kids are using this week.


The Effects of Special Relativity on impulse

Question: Consider a particle moving near the speed of light (let's say 90% of c). It collides with a wall of much higher mass and bounces back. How would relativity affect that impulse value? The two observers would have different values of time for the collision. Does that mean the average force differs between perspective? I understand that the speed at which the particle is travelling is arbitrary, since the effects of special relativity scale all the way to zero velocity. But what would it look like, considering that the effects are so exaggerated at 90% c?
Comment: I would guess that the collision would be elastic, if that's what you're asking.
Comment: I do not understand what you mean by "different values of time for the collision".  Do you mean they assign different *durations* to the collision?  That's not true; the collision is instantaneous in either frame.   Or do you mean they assign different time coordinates to the collision event?  That's true but I can't imagine any reason you'd think it was relevant.  In fact, we don't need relativity for this:  Two observers, one on eastern standard time and one on greenwich mean time, will also assign different times to the event.  So what?
Comment: The collision is not instantaneous in any frame. The classic force versus time graph used to illustrate impulse comes to mind. The collision takes place over a very small amount of time, yes, but it is still not instant.
Comment: Apologies, I was rushed for time on my earlier comment, and it was inadequate. I will attempt an answer asap.
Answer: Yes, indeed, three-force is frame dependent. Look up the Wikipedia article on four-vectors, for example: it gives you a list of quantities that transform in the same way as vectors joining events in Minkowski spacetime.
The four-momentum of a particle is
$$\mathbf{p}=(E,\,p_x,p_y,p_z)=m_0\,\gamma\,(1,\,v_x,\,v_y,\,v_z)$$
where $E$ is particle's total energy, $v_i$ the Cartesian three-velocity components and $\gamma = 1/\sqrt{1-v^2}$ the Lorentz factor (velocities are all normalized so that $c=1$ here).
If this four-momentum is changed by an impulse through an interaction, we get the four force, which is the rate of change of this momentum with respect to the particle's proper time:
$$\mathbf{F} = \mathrm{d}_\tau \mathbf{p}=\gamma\,(P,\,\mathbf{f})$$
where $\mathbf{f}$ is the "everyday" three force, or the laboratory rate of imparting of impulse to the particle and $P$ the laboratory power, or rate of working by the three force. The components of the vector $\gamma\,(P,\,\mathbf{f})$ transform exactly as event spacetime co-ordinates do, i.e. by the Lorentz transformation, so that the three force is frame dependent and gets mixed with the power of the three force when we observe it from different inertial frames. As you can see from the presence of the $\gamma$ factor, the laboratory impulse of the force varies a great deal under relativistic-speed boosts.
How would it look? Bad. Like: really, really BAD!
Comment: Thanks. I do understand the physics and the idea on paper, but I can't wrap my mind around the two experiencing differing forces. When we measure impulse in the lab, what frame would you say we are measuring from? The wall? The particle? Something different? I suppose that in lab conditions, relativity hardly applies, but I wonder which frame would be most "appropriate" to measure from.
Answer: Quantum Theory (lab observation): It would perform the bounce as a particle if there was no observers, but as there are two like you said, the particle would perform as a wave.

https://www.sciencedaily.com/releases/1998/02/980227055013.htm

Being near of speed of light is not being at the speed of light.
Best regards,
Comment: Instead of giving a minus, do answer the question. Is my answer outdated?
Comment: ...What answer?
Comment: haha...you are funny.


Theming a menu - removing a whitespace between the last  and

Question: I want to alter the HTML of the main menu. I have a manu set up with text-align: justify.
Now in Chrome, the whitespace between the last li and ul is rendered as 4px, making the last item not aligned to the right margin. See this stackexchange post. I want to remove the whitespace or replace it with and html comment.
I am a bit lost ;-). What should I be overriding? theme_menu_tree?
I am using the Omega 3.
Answer: Because it sounds like your question is really about how to manipulate the main menu markup in Omega, I guess I'll focus on that. That said however, the "whitespace" issue from the post that you reference is quit strange, as I'm not sure I understand how a newline between an closing li and ul tag would influence any visible alignment behavior. I'm also not sure that Omega even adds any such newlines to the menu output by default. Still, it sounds like you've isolated this as a cause already.
If you are using the main menu that's automatically inserted within the page by Omega (as opposed to displaying your main menu via a menu block or similar), then I believe the most specific theme hook that applies is 'links__system_main_menu'. Check out the omega/omega/templates/region--menu.tpl.php theme file to see how this is ultimately called.
It's important to note however that 'links__system_main_menu' is not necessarily a hook that you'll find an existing theme function for, it's just a suggested pattern. See this post for more on that. Chances are the theme function that's actually getting used currently is theme_links(), or in the case of Omega (which already has an override setup) omega_links().
So if you want to target an override that's specific to just the main menu you could use the code from omega_links() as a template for your own override called MYTHEMENAME_links__system_main_menu(). Then within this new function you could adjust the output to tweak the way "whitespace" is added before and after any ul and li tags as you deem necessary.
Comment: Yeah, for a menu in a block the theme stuff is a bit different. For that I think the hook that applies is 'menu_link'. See [this post](http://drupal.stackexchange.com/questions/7274/how-to-theme-a-menu-block) for more on that. That might actually make more sense within the context of this problem as the default `theme_menu_link()` puts a newline (`\n`) after each `li`, which would seem to correlate with the core issue you have identified. So if you override that function you might just have to remove the `\n` part.
Comment: wow, thanks for such an extensive answer. I'll be working that out very soon.
Comment: I'm trying to apply your suggestions. It uses the `omega_links` function from `omega.theme.inc`. I copied the code from that function to `MYTHEME_links()` in the template.php of my file and it's being overridden. So far so good...
Comment: ...but the main menu that goes through blocks (not rendered automatically by means of primary / secondary links) does not go through that 'theme_links' function...


Did LEGO ever make motorised boats?

Question: Did LEGO ever make motorised boats? Or an official motor that could be attached to LEGO floating boats.
Answer: LEGO had a "Accessory Motor for Boats" included in small number of boats/sets but also released as Accessory Motor for Boats polybag (7099) add-on.
Sets that included the motor in Orange are 7906 and 7899 and in Yellow are 7244, 4669 and 7099 mentioned above.

And here's a picture from Turbo-charged Police Boat (4669) set's instructions showing how to attach and operate the motor.
Answer: The Lego police boat (set 4010, from 1987) had a notch for fitting a motor on the bottom of the hull and it was referenced in its instructions:

The instructions read, in several languages:

In some countries propellor motors (not made by LEGO™) are available from model shops. The notch in the bottom of the hull allows these motors to be attached.

There are other boats with similar hulls: sets 4011, 4012, 4020, 4021, 4022, 4030, 4031.
According to https://www.eurobricks.com/forum/index.php?/forums/topic/156353-boat-hull-motors/ , the notch is compatible with the Playmobil 5159 Submarine Motor:
Comment: I think all the boat sets from that era with a single-piece hull had the notch for a Playmobil motor.
Comment: @Mark I have several boats from that era that all have the mount point.  I figured it was for a motor but I have never actually seen one!

Did LEGO ever make motorised boats?


What is the Arabian Scale in the key of G? What instruments are tuned to the Arabian Scale?

Question: I read about a Native American Flute tuned to the Arabian Scale in the key of G. I know the NAF is tuned to a pentatonic scale but am not familiar with the Arabian Scale. Does it have 5 notes? 7 notes?
Answer: I would assume that the scale you are referring to would be:
G Ab B C D Eb F# G
It is also called Gypsy Major, and in music theory, it is often called double harmonic major.
Enjoy playing with it - it's a really fun sound!
Answer: I googled and found an Arabic scale. In G , the notes would be G A B C Db Eb F G. A whole tone scale, except for the C put in extra instead of going B>C#/Db.
Comment: O.k. if this is wrong, would the downvoter provide a more accurate answer, please, and reasons why it's unacceptable...


Wavelength of light in a waveguide

Question: I've done a derivation showing that the wave length of light in a waveguide is longer than that of free space light. But I don't really have an intuitive understanding of why this is. I think my prof gave an example but i'm not sure I get it. Basically, two waves are propagating down the wavelength. But their angle of propagation is slightly off center. So the intersection of these waves now corresponds to the wave speed? And this is slower than in free space so to make up for that the wave length must increase?
Comment: Without seeing your calculation, it's hard to answer this. It's not even clear to me what you're asking, since of course you can make the wavelength of an EM wave in a waveguide that has a longer wavelength than some wave in vacuum. Are the vacuum wave and the guided wave meant to be related in some way?
Comment: Say you had a microwave emitter. The light has a wave length of 3cm. If you send that light down a wave guide its wave length will be increased to 4 cm. Why does this happen?
Answer: It's better to understand this in the wavenumber domain. The dispersion relation (relating frequency and wavenumber) in a wave-guide is:
$$ \omega_{WG} =\sqrt{(ck_{WG})^2 + \omega_0^2}$$
where $\omega_0$ is the cutoff frequency.
In free space, $\omega_0=0$ so:
$$ \omega_{FS} =ck_{FS}$$
At fixed frequency, $\omega$, you have:
$$ k_{FS}=\frac{\omega} c $$
and
$$ k_{WG}=\frac{\sqrt{\omega^2-\omega_0^2}} c $$
Clearly:
$$ k_{WG} < k_{FS} $$
which means:
$$ \frac{2\pi}{k_{WG}} = \lambda_{WG} > \lambda_{FS}= \frac{2\pi}{k_{FS}}$$
Note that the cutoff frequency means that the wavelength goes to infinity at finite frequency.
Comment: That answer is great and I follow it. But can this be explained without equations? I think that will give me the best intuitive understanding. What is happening in the wave guide that makes the wave length longer?
Comment: Does this mean the phase velocity $v_{phase}$ in the waveguide is faster than light?
$v_{phase} = \frac{\partial \omega_{WG}}{\partial k_{WG}} = \frac{c}{\sqrt{1 + \left( \frac{\omega_{WG}}{c k_{WG}} \right)^2}} > c$
Comment: @A.P. yes, phase velocity is fast than light.
Comment: @David The same way mass means finite energy at zero momentum (thanks to a global interaction with the Higgs field), a wave-guide creates an "effective mass" (via global interaction with the conducting surfaces)  so that there is non-zero energy at zero wavenumber. Check out: https://www.desy.de/~njwalker/uspas/coursemat/notes/unit_2_notes.pdf
Answer: Here is a way of thinking of this a little more intuitively, which might help.
The waveguide has a characteristic impedance which is different from that of free space. Therefore we expect that the propagation velocity of an EM wave in a waveguide will be different from its free-space value. And indeed it is; it will always be a bit slower in the waveguide than it would be in free space. As a consequence, the wavelength of an EM wave propagating down a waveguide will be slightly longer than it would be in free space.
This has important practical consequences.
The original SLAC beam tube was a waveguide 10,000 feet long, at the head end of which electrons were injected at very nearly the speed of light. From there, the electrons rode the crests of a wave train of microwave radiation propagating down the beamline, which did little to increase their velocity but increased their energy enormously. To do this, it was necessary to precisely trim the impedance of the waveguide so the propagation velocity of the EM waves in the tube would properly match that of the electrons, in every segment of that 10,000 foot long tube. This was done essentially by hand on every subsegment of the tube after it was fitted together but before it was installed in the beam line.
The result? Nobel prizes!
Comment: Thank you, this does help a lot. But could you speak more to impedance? As far as I know its just the ratio of electric over magnetic field ratio. Does a lower impedance mean a faster wave? Are there any other reasons we would want low impedance?
Comment: Have a look at the wikipedia article on waveguide *velocity factor*, it explains this stuff much better than I can.

Wavelength of light in a waveguide


I can't play the trumpet after a year: reading notes, playing on the same valve

Question: I play the Trumpet for school and I'm done. I started to learn B's and B flats and Low C's and highs C's and sharps and it all became a blur. Most of the notes are played on the same valve so I'm lost. I can't play when they're on the same valve because I don't know what those notes sound like. I've been playing this for a year and every time I can't play with the class because I don't know what the song sounds like. My teacher tells me to play louder and I can't play it at all. Worst of all I still can't read notes! My notes also sound so raspy and I can't hit high notes. Next year we're going to be playing from an even harder book but I don't know what I can do. I also can't go to Trumpet lessons because my parents can't afford it.
Comment: A year is a very short amount of time on a musical instrument.  It's normal that you're struggling. If you keep at it, you will overcome each problem, possibly one at a time and it may take a few years.
Comment: Sounds like you need to work on embouchure, breath control, scales, and reading music. It needs practice, no way around it. Watch tutorial videos on youtube. I've tried and failed to even play a note on trumpet, so good luck!
Comment: What is the title and author of the book you're using?
Comment: What exactly is your question?
Comment: @mkrieger1 I think the question could be as simple as, how do I get started without a teacher
Answer: Number one, do you want to play the trumpet?  If so, read on!  I ask this first because you will only improve if you work at it, and you are only likely to work at it consistently if you want it.

Put down the book.  You don't need it yet and if reading the notes is too hard for you it's not doing you any good.

Put down the trumpet.  All it does is make the sounds you are making into the mouthpiece louder, and if you're not doing that right your trumpet will only make a poor buzz sound like a loud poor buzz.

Pick up the mouthpiece, sit up tall, take a good breath, and buzz for as long as you can.  Try to make it steady,  strong, and full.  It will sound like a buzzing mosquito or a crazed duck.   Do this many times, each time for as long as you can keep it going.

Again with the mouthpiece alone, buzz but see if you can make it go up and down in pitch like a siren.  Higher notes take more air, focused more.  Repeat until you can make a smooth siren from low to high ad back down again.

Now try to play a song, still mouthpiece only.  Start with easy, little kid songs.  Mary Had a Little Lamb.  Hot Cross Buns.  Claire De La Lune.  You are learning to use your air/tongue/lips to create high and low notes, and this is how trumpets work.

When you can do this,  try to find these songs in the book.  Follow the instructions for which valves to press down for each note and you're on your way.

As for the band teacher,  tell them that you want to be a trumpet player and you're working hard. Tell them how much you practice and what you have been working on.  They are probably over-scheduled and can only teach you in large groups, not one-on-one.  Can you offer to spend recess/lunch/after school with them once or twice?  If they are worth their salt they will recognize your efforts and move heaven and earth to get you going.


What are the signs that an interview went well ( or badly )?

Question: I have been attending lot of interviews recently as a new graduate. What are the signs that one can get from HRs and interviewers that the interview well ( or badly )?
Comment: Signs that it went well? You get the job.
Comment: Hey Surya, and welcome to [workplace.se]! As-is this question has been voted by the community to be too broad because it is a bit too open-ended. As explained in our [help/dont-ask] open-ended questions aren't the best fit for our format. Is there any chance you could [edit] to focus on an practical answerable question based on actual problems you face? Thanks in advance!
Answer: It is easier to tell if it went badly than if it went well. The sign that it went well is when you get a call back for another interview or a job offer. The best interviews you have may not result in moving further into the process because you are competing with others and someone else may have been much better than you were. So even if you feel good about what you said, it is not a sign that you are getting the job.
Signs it went especially badly are if they cut off the interview rather abruptly, if people seem to be going through the motions and not paying attention to what you said or if you know that you very badly missed the answers on several questions.
Answer: I am a fellow job seeker too. I feel if they say a time scale by which you will hear from us, I think it is a good sign that they are thinking about the next step. Another thing is showing around the building. If they are willing to put an effort to show you around the building, then that is a good sign.
Answer: A sign that the interview went well is when the interviewer(s) tell you what next steps are before you ask - they may already be envisioning you moving to the next step!


Work that I reasonably do without publications post Ph.D (R2 university)?

Question: I'm a fourth year student in an Experimental Psychology Ph.D program with an accepted MA also in Experimental Psychology from a different program. I'm posting here since I'm about to graduate in May 2024 without any publications and only got a conference poster in 2023 and should have another in 2024 during my Ph.D. I plan on trying to get my dissertation published at some point after I write it up completely and defend it.
Long story short, after some reflection on this post I made months ago, I agree that there's a general lack of productivity: Conference, poster, and publication gaps due to COVID and poor advising. How to explain for the future?
All throughout my time in graduate school, I didn't work on multiple projects first a variety of reasons. During my MA, I waited on others to tell me it was important since advisors were a thing (I had no idea that they did not work that way though). First two years of Ph.D, my advisor told me she wanted me to focus on just elective coursework (year 1 of Ph.D only) and my project to qualify for candidacy. Now, I can't say I have much of a reason other than poor stress and emotion management to the point its affected my energy levels and I've found myself not eating a lot and taking frequent naps. I've noticed some improvements health wise lately, but my cognition (or "brain fog" as some call it) is horrible. I'm neurodivergent (autistic, ADHD-I, and dysgraphia) as well, which is another reason why. I'm convinced I've experienced autistic burnout for a little over a year and that's a big reason why (and processing the ambiguity alongside struggling with self guidance). I'm also a full time visiting instructor at a small liberal arts college since my funding ran out this academic year and that's taking a toll on me.
After discussion with family, friends, and peers, I'm cutting my losses with this line of work and want to move on to something else. I'm not dropping my Ph.D since my fellowship I have mandates that I graduate or I have to return $11k to my state. The reason is because, for me to get autistic burnout, I have to keep doing things above what I was sustainably capable of for an extended amount of time. The fact I achieved so little during my Ph.D (other than my fellowship and visiting instructor position) and got burnout is what's telling me I need to move on. I saw another answer in my last post mentioned a lab tech, which is something I wouldn't mind doing (eye tracker hardware, software, and E-Prime 3.0 for experiment creation) at all if there is a job market like that in the social scieces or in other fields.
I do not want to do a postdoc given that I don't have a publication record at all and that I likely won't be able to produce enough in the same way I wasn't very productive during my Ph.D. I think if I had something with clearly defined performance outcomes and was less ambiguous as to whether I know I'm doing well that would be ideal (e.g., a lab tech position since I know what a finished product would look like in this case). One example I can think of is someone who graduated with just their MA from my current program and became a research assistant at eXponent, a major company. He's essentially doing the research assistant and lab management work for a private company that recruits participants. I could see myself doing something like that. I'm just not sure if I'd have the qualifications given lack of publications and low Ph.D program productivity though.
Welcoming any thoughts or opinions.
Comment: @MichaelMcFarlane I'm against a postdoc because of productivity concerns. If I'm already at my capacity just by teaching and data collection alone (not even writing because I was too burned out to write), then I'm confident I might get fired because I'm having difficult managing multiple projects at the same time. I'm barely keeping it together with full time teaching on top of all of this. To be honest, I really don't know how I'm going to make it through next semester even. I need the money and to build my CV with this gig but I achieved very little still.
Comment: I've never heard of Experimental Psychology, what sort of work does it usually lead to?
Comment: @Kilisi I have two notable examples but its not generalizable (I'll explain why here in a second). Many of those who have an Experimental Psychology background become data analysts in fields that require analyzing survey data or something similar. Others who have a ton of publications become professors or work in academia (but they generally come from an R1). I am a bit of unicorn because I only two took statistics grad courses. That said, Experimental Psychology is not exactly generalizable at all because someone has the flexibility to develop niche skills. Hope that answers your question.
Comment: Does you institution have resources or support for neurodivergent folks
Comment: Are you against doing a postdoc solely because of your productivity concerns? Or, rather do you not feel like doing one?
Answer: You don't actually say in your question what you do want to do, only what you don't.
Consider abandoning academia entirely and moving out into "real" work.  Once you leave academia, nobody will even care what papers you have published.  You then have the opportinity to find a career that suits you and the skills you have.
Comment: @simon_B I do want to become a lab tech or a research assistant of some kind. The guy I knew at eXponent was the example of what I would like to do.
Comment: To get a lab tech position, simply start applying to companies that have those positions. It may take a bunch of applications, but the more you apply, the more likely you are to get such a position.


Master pages in asp.net ? Execution of Master pages?

Question: In asp.net, i have taken one master page, 4 four child pages and one login page, which is not in a master page. My question is when a user login redirects to the page which is has master pages, is master page execute every time or only one time after login.
Answer: Master-page-engine is just part of total page life-cycle. (see for full list of taken actions there: http://blogs.thesitedoctor.co.uk/tim/2006/06/30/Complete+Lifecycle+Of+An+ASPNet+Page+And+Controls.aspx)
So short answer - yes, each time page derived from master is shown - master is executed.
Answer: A master page is executed every time a requested childpage has it as it´s parent.
So if you go to your loginpage without master and then redirects to a page with the master, the masterpage is executed once. If you later request another page with that master  or the same page again doesn´t matter. The masterpage will be executed again.
Study the ASP Page lifecycle as the masterpage has some strange behaivor and acts mote like a subcontrol. You have to be a bit careful with some events.


Setting fonts in Firemonkey

Question: Is there a way to set font properties in the firemonkey style editor?
I tried both using a custom style and changing the default style of a TButton.
Each of these layouts have a child TText component which is named text. If I try to change the  font settings (e.g. change the bold flag) it looks okay in the designer, but in the form designer as well as at runtime, nothing changes.
Is there also a way to define a default font for all TTextControls? In vcl there is a parentfont property which is not available in Firemonkey. After a closer look to the components code, I think it should be possible by defining the text layout for a TTextControl in the stylebook. But this component is not registered in the component palette.
Update: TMenuItem does not apply font settings at all. At the moment it can only be done at runtime.
Answer: This was fixed in XE 2 Update Pack 1. Try downloading the new version. You can now set Font styles.

Setting fonts in Firemonkey


Low water pressure in the early morning hours

Question: Good morning. I am having a real problem that no on seems to know how to fix. In the early morning between 4 am and 7 am I have no water pressure. It is impossible to take a shower. The whole house has no water pressure. At first I thought it was the sprinklers outside that went on from 1-3 am that was the cause of this. The sprinkler system has been cut off and I still have no pressure. Please help. Also note, no one else on my block wakes up at 4 in the morning to shower and no one else on my block has experienced this problem. PLEASE help. This is ruining my mornings!!! Thank you !
Comment: Assuming you have city water service and not your own well.  Is this problem new?  Have you always lived there? Or is this the first summer?  Is your house geographically higher up (hill) than most?  You mention your irrigation system has been turned off, but do you neighbors have irrigation systems?  Our house is at the top of a hill, during high volume peak water usage hours in the morning there is no question our pressure drops, not as much as yours.
Comment: Have you tried contacting your utility?
Answer: Check that the water softener hours for running and doing it back flush (if you have one).
If it is not a running softener, a water pressure gauge that attaches to your hose bib is a fairly cheap purchase.  If you obtain one hook it up to your hose bib and record the pressure low values and what you consider normal values.
Then obtain permission from one of your nearest neighbors to attach it to their hose bib.  And record the pressure at the same time you had recorded your values.  This will isolate if it is just your home or the whole neighborhood.  If it is the whole neighborhood take the readings to your water service provider and request them to investigate.
Comment: Thank you Niall C. I had to have missed the save on last changes fixing the spell checks and proof reads.  I will have to work harder at that.  No excuse, but cancer related infusions make some days not work as I like.


Why does this planet (J1407 b) and Saturn's ring center on its equator?

Question: Why is the material in J1407 b's or Saturn's rings stay in a disk not scattered? Is it the gravity and/or magnetic field that causes this? Does it differ with other large bodies that might not have a electromagnetic field?
Comment: Related: http://physics.stackexchange.com/q/12140/ http://physics.stackexchange.com/q/6545/ http://physics.stackexchange.com/q/26083/  links therein.
Comment: Which equator?  The geographic equator defined by the spin of the planet or the orbital equator or the magnetic equator?  Regardless, the answer is almost certainly going to be about angular momentum conservation...
Answer: Saturn's rings are rather interesting. From what I've read, the different layers of dust and rocks have been formed over millions of years, by a phenomenon known as orbital resonance. Orbital resonance is something like an increased(or decreased) gravitational effect due to 2 bodies moving with certain time periods. This effect causes  stability in some cases, and instability in others. When there is instability, there is an effect known as 'clearing the neighbourhood' , in which the unstable objects undergoing orbital resonance, are flung out of their current orbit, unless they find a more stable one. That's how the rings arranged themselves in bands, and are not continuous.
For more info, read this : orbital resonance
Correction: clearing the neighbourhood is not the name used in this case. It is used for the removal of unstable orbits in larger systems like the solar system.
Comment: The OP does not ask why the material stays in rings, but why it stays *in a disk*. i.e. why does it remain in the same 2D plane? Perhaps that's not what they meant, but it is what they said.
Comment: It is not true that all the orbits lie in the exact same plane at the exact same time. There are small angular perturbations of one plane with respect to another. Orbital resonance is also a factor in keeping them in the same plane
Comment: That is they are in the same plane on an average.
Comment: Hmm okay. It seemed to me like your answer was simply addressing the reason of why the disk splits into rings.
Answer: The reason it's a disk and not spread out is actually simpler than you might imagine.
Consider all of the mass in the system as a whole. It will have a certain centre of mass, angular momentum, etc, which much be conserved no matter how the distribution changes. That defines a preferred axis of rotation, and perpendicular to it, a plane that is the natural direction for a ring.
Now consider any mass that is not, initially, in that plane. Say a rock that is travelling around the centre of mass "top to bottom", in what would be a polar orbit around a planet. By definition, there is some other mass with the opposite direction on average. So if you wait a couple of hundred million years, the objects that were orbiting top-to-bottom will eventually meet one travelling bottom-to-top, their non-plane momentum will be cancelled out, and any remaining momentum will be in the plane.
That gets you something like a disk. After that other issues come into play that can shepherd or randomize the distribution. In the case of a ring around a large planet, like Saturn, the equatorial bulge helps out.
It is entirely possible to construct rings that don't spin the same way as the planet, but they will tend to scatter. There has been some work on using such a system, with artificial shepherds, as a way to build a skyhook.


Is acetone safe and effective as a lens cleaner?

Question: I recently came across a clip on youtube which showed the process of making camera lenses. I noticed them using acetone as a lens cleaner. My question is how effective is acetone as lens cleaner? Will acetone damage the coating on the lens?
Answer: Here's Bob Atkin's answer on the topic and I generally agree. In a nutshell, don't use it unless you really know what you're doing and have it sourced. As a general rule of thumb, use lens cleaning supplies specifically made for lenses and don't get too paranoid about the front element being clean. Seriously, it takes quite a bit to really mess your image quality and it isn't necessary to be fastidious about it.
Comment: +1, I would say Bob Atkin's answer is definitive. Acetone is a powerful solvent and should never be brought near a lens assembly. Ethanol is hygroscopic and will often contain quite a lot of water which leaves drying marks. One can buy the pure, reagent grade, water free form of Ethanol, but it is rather expensive. We used this in the metallurgical laboratory when preparing polished metal specimens for viewing under a microscope. It has to be critically clean in this case.
Comment: +1.  Even with a whole [fly in the lens, you couldn't see it](https://petapixel.com/2019/04/11/the-mystery-of-the-fly-in-the-2100-weathersealed-lens/) until stopped down pretty far!
Answer: You'll note that at the point they did that, it was just a glass blank. What will the acetone do to the glass and coating? Pretty much nothing. What will it do to the rubber gaskets that seal the dust out of the lens? That's the real question to me. Having worked around fibre-glass for a few years, which uses acetone in pretty large quantities... well, I wouldn't be putting it into contact with anything rubberized that I cared about keeping the rubber in good shape... it just seems to dry it out way too fast and lead to cracks. Just not worth it to me, especially when we are talking about the outer surface of the front element.
Comment: I'd also be worried about the glues used to hold things together in many lightweight (plastic) lenses, as well as the lens barrels (which are often plastic or coated in plastic).
Answer: Acetone is an excellent solvant for some plastics. I've tested it with styrofoam once here :)
It does clean pretty good though.
For my filters (polarizer etc.) I was most successful with liquid soap and water. Not everything works, but there are liquid soaps which do not leave any stains (and which I'm using for my glasses as well now :)). Also works for lenses, but then you should not pour water on them directly but use a wet towel.
Edit: Generally about alcoholes for cleaning. I tested them a little bit, Alcohol and Isopropyl alcohol, mixed with water.

Isopropyl always smears. Iff you hold the cleaning towel with your hands. The reason is that it will solve grease from the fingers and evenly distribute it on the surface. The solution is to use something grease-free for holding the towel (or whatever it is).
Alcohols alone dry too quickly and leave stains.
Water alone does not solve greasy particles.
The best way to clean with alcohol based liquids I've found so far is to use water with some drops of alcohol (one of the above); the alcohol will bind greasy particles, the water will prevent the liquid from evaporating too quickly, so the drops can be removed easily and without stains using a dry towel.
Answer: Avoid using acetone on lens assemblies. It is a solvent and it acts on the components destructively.
It is not possible to predict what specific parts will be affected.
Note that a glass lens (singlet) is not the same as a lens assembly made of and with many different materials both organic and inorganic.
The first things you'll notice is that the paint and varnish used for the finish and engraved/etched fillings will soften, swell, and possibly lift before being dissolved. The serial number and lens information such as aperture and distance marks will be removed for example.
This is not a good idea. Instead, use materials and processes suitable for the equipment.
Answer: Acetone is a killer solvent.  It's basically identical in behavior (and at least formerly in formulation) to nail paint remover which will soften and dissolve dried paint layers.  You don't want even the fumes to come anywhere close to your camera.
Rubbery surfaces supposed to have a friendly touch can bleed out stickiness after a decade or so.  Alcohol and a cloth can be used for getting the surface dry enough that it will be good for another few years.  Use acetone instead, and the rubber will come off, as will the paint and plastic below it.  It's a sledge hammer for working with plastics, and you would use it for working on a lens just as comfortably as working with an actual sledge hammer.
There may be uses in controlled parts of the production on parts not yet assembled with other parts.  It may even be used in the process for getting the plastic parts molded.  But it doesn't belong anywhere near an assembled product.
Answer: I soaked a Canonet GIII front outer element for two days in acetone. Nothing looked any different after I removed the element and dried it off. All the coating was still intact along with the fungus it had in the beginning
Answer: I use a variety of liquids on cotton swabs: naphtha, isopropyl alcohol (99% or 91%), and Zeiss lens cleaning fluid. I also use breath moisture. If oil in the lens has migrated to the glass, I remove the affected element and soak it in a small dish of water with a couple of drops of dissolved dish soap.
Acetone is a rapid solvent for ABS plastic. Almost any black plastic on a photographic lens is ABS. I have never used acetone on glass because I think naphtha probably achieves the same result, and does it safely. It's a good solvent and I have never seen it cause harm to coatings or glass.
Most inside coatings are hardened, but some can be quite soft. I am still working on how to avoid scratching inside coatings.
To treat mold (aka fungus, but not actually fungus) I use hydrogen peroxide and ammonia, 1:1 and let it stay on the affected glass for about 20 to 30 minutes. The mold tends to disappear, but if you breathe moisture on the lens where the mold was, you can usually see a tracing of where it was. But the H2O2 + ammonia mixture is supposed to kill the mold and any spores.
Comment: (Mold *is* actually fungus.)
Comment: What do you mean by "not actually fungus"?


Both Schedule C and Schedule C-EZ form for freelance taxes?

Question: Do I submit both or... which one? (If it is just one) I have been searching for solid information about this for a couple of days... Decided to just throw this question on the stack. Maybe the answer will help others too.
Answer: You file one or the other per business, the C-EZ is for simpler situations and can be used if you have profit from your business and meet these criteria per the IRS:

Your expenses are not greater than $5,000
You have no employees
You have no inventory
You are not using depreciation or deducting the
  cost of your home

If any of those criteria disqualify you from using the C-EZ you'll have to file the standard Schedule C instead.


I feel something uncomfortable with Haskell record syntax

Question: Most of Haskell syntax has beauty of purity. But the record syntax looks ugly. It's uncomfortable. It feels some kind of mixture with C. It requires comma and braces. Haskell has tab,line based separation. So it looks too verbose than originally it requires. Why is it designed in that way?
Comment: You aren't alone. Quite a few people complain about (the current incarnation of) records.
Comment: To me all of Haskell feels weird. What can I do?
Comment: Eonil: If you *really* hate record syntax, you can disable it with the {-# NoTraditionalRecordSyntax #-} GHC extension.
Answer: While I wasn't on the design commitee, I reckon that record syntax was shaped to be consistent with list syntax. Module export syntax uses commas, too, the only real place where layout is used is top-level declarations, where clauses and do-notation.
On top of that, given
data Foo = Foo {bar :: Int, baz :: Int}

writing
fnord x = x { bar = 4 }

without the braces would clash with the rest of the syntax, and using layout, like
fnord x = x
    bar = 4

would make the syntax quite brittle. Add a "where" in the wrong place and your code means something completely different.
If you're not happy with the state of records in Haskell (and you wouldn't be alone with that), I recommend you have a look at fclabels or even elaborate typeclass hackery like HList or grapefruit-records (the latter two not being for the faint of heart, but also insanely powerful)
fclabels would allow you to write (yay pointfree)
fnord = setL bar 4

as well as
getBar = getL bar

on top of it's actual raison d'etre, which is composing labels:
 data Person = Person { _place  :: Place, ... }
 data Place = Place { _city :: String, ... }

 moveToAmsterdam :: Person -> Person
 moveToAmsterdam = setL (city . place) "Amsterdam"

Comment: Not at all, you're going to get another (sharing) copy of the record with a single field changed, just like with record syntax. No mutability or break of referential transparency involved.
Comment: Hmm. Does `setL` mean mutable?? Without IO? IT's hard to understand...


I INSTALLED THE OS BUT I DONT KNOW HOW TO CHANGE FROM WINDOWS TO ELEMENTARY

Question: I installed elementary os, but I don't know how to go from windows to elementary, and in the list of systems it doesn't appear
Answer: what do you mean by that exactly? Is elementary invisible in your BIOS? What happens if you select the partition that you installed it on?
If it just stays that way check if you have FastBoot enabled and Legacy Boot disabled. However I would require more detailed information for further assistance.


Skyrim PS4 edition cheat codes

Question: Are there any cheat codes (certain combinations of buttons, etc.) on the PS4 edition of Skyrim? I was hoping there might be a code that gives me a jump boost or reduced fall damage, as I'm currently stuck on the side of a mountain with no way up or down.
Comment: Should have brought a horse.
Comment: A couple of options:Fast travel to get out of there.  If you cannot then just reload from a previous save.  If you have the whirlwind sprint you can use that to move to another place.
Comment: @Iszi Lol, I don't have a horse. I've just started a new play-through of the game.
Answer: No, there are no cheat codes. On Windows, you can use the console, but that isn't possible for the PS4.
As fja3omega mentioned in a comment, your best bet is probably to use fast travel to move somewhere else. You could also try to run/jump sideways along the rocks and get to somewhere more convenient.
If you happen to know the Become Ethereal shout, just use that and then jump off the cliff. You'll survive the fall no matter how far it is.
Comment: Haha, well that's one way out of that situation. :p
Comment: Well, where I was at on the side of the mountain, I wasn't able to fast travel. It said that I was falling/jumping. And I don't have that Shout... I actually don't have any Shouts yet. Thanks though!
Comment: Oh, I haven't experienced that. Maybe you were slipping on the rocks or something, so the game thought you were falling. I hope you figured something out, anyway.
Comment: I did. I decided to die lol.
Comment: Lol yeah. I am actually level 100 in all my skills already, but I don't have Shouts yet. I chose to use the method where you run around the entire map and discover all the locations you can before you do the Bleak Falls Barrow quests. This way, I won't encounter any dragons and will be able to fast travel anywhere I need to go, rather than having to walk and then ending up having to fight dragons on the way. So, dragons aren't appearing in my game, so I can't get souls to activate the few Shouts I've learned.
Answer: There are mods for PS4. Just press "mods" if you are logged in and then you will find them.
Comment: Welcome to Arqade! Could you elaborate on this?
Comment: I know there are mods. However, at the time I posted this question, I still had not fully beat the game, and had no interest in modding my experience.

Skyrim PS4 edition cheat codes


InDesign - Show/Hide multiple forms on different pages with one button

Question: I'm trying to create a multiple language interactive document in Id. So far I can create flags (language buttons) that can toggle on/off languages (different frames) on one page, but is there a way to do this throughout the document with one click?
Answer: It depends on what you are up to. If you want to work with different languages within the indesign document, you can either choose to work with one layer per language or use conditional text.
However if you want to have such a language switch in outputed document such as a PDF or an ePub, then it's tougher because you can't change InDesign layer visibility in such formats. Maybe a script in the Acrobat side may manage it to the condition you actually create a PDF that embeds layers.
You could use also state objects but that wouldn't apply to PDFs.
Comment: This is just the tip of the iceberg, because I need to extract the HTML5 from the ePub file, but like you wrote it will be hard to change layer visibility without a script.

What I'm trying to do is create a presentation in HTML5 to import in Adobe Captivate, because Captivate is a very bad designing tool. All in all I'm trying to develop a workflow from a program like InDesign or other, import it in Captivate to maintain SCORM compatibilities and place it in Moodle.


How to mount a VHD which is on an external USB hard drive

Question: I have Virtual PC 2007 and I have a VHD on my external harddrive.  The vhd is from a complete Vista omputer backup.  When I follow the wizard it gives me two options both relating to compacting the VHD.  Is there anyway I can simply mount it, AS-IS .  Not sure if it will matter but,  the VHD is 150GB and the temp computer I am currently on only has 23GB of free space which is why I simply want to mount it and use as is.
Answer: If you are running Windows 7 this can be done using Disk Management.

Open Computer Management
Select Disk Management
Right Click on Disk Management
Select Mount a VHD file

However if you are running anything below Windows 7 this is not supported.
Comment: lol fantastic!  just installed a fresh copy of Windows 7 and this is great news.  Needed a break I tell you.  heers will post back an update. +1 and will answer shortly.
Comment: ok I have done that,  it says it is not intialized.  How I can do that?
Answer: If one is using pre-Windows 7 operating systems (e.g., Windows XP or Windows Vista), this can be done using the utility vhdmount, which comes with Virtual Server. Virtual Server is also a free Microsoft product and can be installed to get one's dirty little hands on vhdmount.
One caveat is that one has to run vhdmount from a command-prompt with elevated permissions, otherwise it keeps failing silently. So what you would do is, right-click on the command-prompt icon in the start menu, and then select "Run as Administrator", and then issue the vhdmount commands at that prompt.
Please pay special attention to the command-line parameters of vhdmount, as you can mount a VHD file and have vhdmount discard all changes to that disk image when the disk image is unounted. Of course, if you are saving your PhD dissertation to that mounted VHD image, and all changes are discard, that might be detrimental to your blood pressure :)
Therefore, first run a simple test to familiarize yourself with vhdmount.


What is the recommended way to embed a react.js webpage in an account record and it communicates with it?

Question: A client needs an external react.js page embedded in account records but it needs to interact with the account page. For example, the react.js page needs to display data from related records of the account record that it is embedded in. Firstly, can this be done? If so, what would be the recommended way to embed the page in an account (lightning component? lightning web page that is a wrapper to the react.js page?) and can it communicate with the account related list records?
Comment: At a high level, this seems like a painful choice for means of integration. I suggest you pursue an approach where all your UI elements are native to Salesforce, and you pull in any data you need from the external system via other means.
Comment: I accept what you said but we need the same page to be accessible on an external website and the IT team knows react.js well. They want to use the same page inside the SF account so an internal employee sees the same data and there is only one GUI interface and if changes need to be made, it's in one place. Can you think of any other way to doing this correctly?
Comment: Just to give a full picture, each account has a child object called subscriptions. The client wants to allow their customers to login to their external site, and view their subscriptions and made changes or whatever and if an internal employee needs to do this for the customer, they employee can go into the account, view this react.js page and make the changes for the customer themselves. Does this make sense?
Comment: You're going to have to explore [`message`](https://developer.mozilla.org/en-US/docs/Web/API/Window/message_event) listeners and [`postMessage`](https://developer.mozilla.org/en-US/docs/Web/API/Window/postMessage). You might hit security roadblocks you can't work around, so I would be leery of saying it will work for sure, but you at least can specify `targetOrigin`.
Answer: The only tool you really have here architecturally is to use window messaging. Both components will need to add  message listeners. Once you've done that, you should be able to postMessage between them to communicate. I wouldn't say it's the "best practice" here (which would be to avoid framing in external pages), but it might work for you.


Would I say... I'm not at your convenience or I'm not at your convenient?

Question: Things don't just happen when you want it to.
How can I put that in a sentence with the word convenience  or convenient?
Answer: Although at your convenience sounds a little better, both are an awkward way to phrase it. A better way may be to say:
I'm not available at your convienience

Since a person cannot be at your convenience, this makes more sense.


"this" keyword in event methods when using JavaScript prototype object

Question: I'm trying to access the member variables of a prototype class in JavaScript in an event handler -- something I'd typically use the "this" keyword for (or "that" [copy of this] in the case of event handlers). Needless to say, I'm running into some trouble.
Take, for example, this HTML snippet:
My Link

And this JavaScript code:
function MyClass()
{
  this.field = "value"
  this.link = document.getElementById("myLink");
  this.link.onclick = this.EventMethod;
}

MyClass.prototype.NormalMethod = function()
{
  alert(this.field);
}

MyClass.prototype.EventMethod = function(e)
{
  alert(this.field);
}

Instantiating a MyClass object and calling NormalMethod works exactly like I expect it to (alert saying "value"), but clicking the link results in an undefined value because the "this" keyword now references the event target (the anchor () HTML element).
I'm new to the prototype JavaScript style, but in the past, with closures, I've simply made a copy of "this" in the constructor:
var that = this;

And then I could access members variables in event methods via the "that" object. That doesn't seem to work with prototype code. Is there another way to achieve this?
Thanks.
Comment: Responding three years late :) But for posterity: I was referring to straight JavaScript prototypical classes.
Comment: Are you referring to the Prototype library or rather straight JavaScript prototypical classes?
Comment: Possible duplicate of [How to access the correct `this` / context inside a callback?](http://stackoverflow.com/q/20279484/1048572)?
Comment: @Bergi: For the record, I asked this question in 2009. The question you linked was asked in 2013.
Comment: @Michael: Yeah, but that doesn't matter. Dupes are closed by quality of answers, not by date; the one I linked is the canonical question on loosing `this`. I wasn't sure whether it's an "exact" duplicate, that's why I haven't just closed it but only commented. The link is definitely helpful to everyone who visits this question.
Answer: You need:
this.link.onclick = this.EventMethod.bind(this);

...'bind' is part of Prototype, and returns a function which calls your method with 'this' set correctly.
Comment: How does `onclick` get access to the event interface?
Comment: @Karl By "access to the event interface" do you mean "receive the event object as an argument"? The `bind` method **returns a function** (with a fixed `this`), so `onclick = this.EventMethod` is basically the same as `onclick = this.EventMethod.bind(this)`. In both cases, you store a function in the `onclick` property; they're identical in terms of how their arguments are handled. If your question is more generally about how arguments are passed to listener functions, that's quite a different question than what's being asked here, and you should ask a new question.
Answer: Your "that=this" closure idiom is still applicable:
function MyClass()
{
    ...

    var that = this;
    this.link.onclick = function() {
        return that.EventMethod.apply(that, arguments);

        // that.EventMethod() works too here, however
        // the above ensures that the function closure
        // operates exactly as EventMethod itself does.

    };
}

Answer: You should try
this.link.onclick = this.EventMethod.bind(this);

Answer: As stated above, using bind which is a part of the Prototype library is a clean way to solve this problem. This question is a duplicate of another SO question which is answered here with implementation of the bind method without including the whole prototype library :
https://stackoverflow.com/a/2025839/1180286
Comment: That question uses JQuery. I'd much rather see a pure JavaScript question / answer be the standard.


How do I buy games in the form of PSN codes?

Question: I'm fairly new to PlayStations in general and was wondering how I can buy a game from the PSN in the form of a code? For example, if I buy ClaDun x2 or some other game, instead of it going to my account, I want it in the form of a redeemable code that I will probably give to somebody in the future, like a gift, or probably to trade with their other games? I came from Steam so I'm not sure how Sony does it in their system.
Comment: I don't think there's such a thing as gifts on the PSN, but you could buy a PSN funds card and gift it to someone. Whether that person buys the correct game or not, however, is a different story altogether, I'm afraid.
Comment: You found a solution? Is it still valid?
Answer: You can get codes trough third party sites. I know you could get PS4 game codes on Amazon, looks like its available for all the PS4 games(Amazon.com)
Them might as well sell codes for PS3 but I doubt it. Never encounter this alternative buying games for the PS3
Answer: Not sure if they still do but Gamestop sells DLC and you get a redeem code on the receipt. They don't sell all DLC though.
Comment: No I don't mean DLCs, I mean full games.
Comment: They sell full games too as DLC. Just not all of them.
Answer: If you go into GAME stores they sell specific cards with download content on. They also sell them as a bundle sometimes on pre owned games. They stick the card in the cover to buy both at the same time.


What is the cause of Muṣitasmṛtitā?

Question: I have read the causes of anger, lust, etc. but I haven't yet encountered the cause of Muṣitasmṛtitā. I am sure, most of us have had issues with this ailment.
What is the root cause of it?
Answer: If you read my answer to question about attention, you will see how I explain the process of attending, which is exactly what you're asking about.
From this explanation it becomes clear and almost obvious, that the cause of losing attention is that some other stimulus creates more active associations in you than the object you're trying to attend to. So those new associations crowd out perceptions and thoughts about the original object, and so you switch the focus.
The root of the problem is, you have more interest in other topics than in the object you're trying to focus on.
Maybe you have inner resistance/aversion to this object. Maybe you are lazy because you don't believe in success of your exercise. Maybe you are simply not familiar with the object of meditation and so you have nothing to think about it. Either way the object is not creating enough reaction in you to remain engaging.
One way to fix all this, instead of forcing your attention to stay there by force, is to do active investigation of the object you're attending to - to examine it, look at it from all sides, compare it, analyze it, research it, examine your attitude to the object, - and this way you will generate a lot of associations leading back to the same object, and so your attention will remain with it.
Answer: The root cause(s) would be lack of mindfulness (which, incidentally translates to right recollection in english), and lack of concentration (samadhi).
Going deeper in analyzing the root causes(s) one could argue that the three poisons greed, ill will and ignorance plays a significant part. On the other hand, they are perhaps a bit more distal causes.

What is the cause of Muṣitasmṛtitā?


Justifications for different Monte Carlo trial moves

Question: Why do we perform different trial moves in Monte Carlo simulations in Statistical Mechanics? For example, in NVT ensemble simulations, Why only atom displacement moves? In NPT ensemble, why do we need to perform both volume adjustment moves and atom displacement moves? What are the variables that we are minimizing ? What are our main objectives behind performing these trial moves?
Answer: The question is basically about the Monte Carlo move set, and their choice.
The Monte Carlo method basically requires that the system diffuse in the "phase space". This is done by first suggesting a move and then calculating the probability of acceptance of such move. This is to say that the move set will have to "satisfy" the conditions of the simulation. If you are doing constant-N,V,T simulation, the condition of constant volume will of course preclude the changes in the volume. If you are doing the constant- N,p,T simulation, the volume has to be changing so that each sampled phase point have "same" pressure. In both NpT and NVT , the particles are neither destroyed or created.
The main objective of the any move in the move set is to allow for various "ways" for the system to move about and to (and into) new regions in phase space, also called sampling. For mono-atomic simulations (i.e. noble  gases), it is natural to think of the simplest move: displacing each particle independently. This does not mean that other MC moves are not to be considered; of special interest are what are called "collective moves" where more than one atom is displaced together/nearly together. For example: if you are simulating water, then you will move all the three atoms (the two hydrogens and the oxygen) belonging to the same water molecule together. If not, most of the moves that you make will take the system to configurations having very high energy, and will be rejected; and the system will only diffuse very very slowly in phase space. For water system, it might be prudent to have a rotation move, where the molecule as a whole tumbles randomly.
What is the variable that is "minimised" ? This is tricky. The common lore is that the variable (in the move) be tuned so that 30-50% of the moves are accepted. For example, in the dispacement move, the variable is the maximum-value of such random displacement.
I would suggest the book by Allen and Tildesley "Computer Simulation of Liquids", Chapter 4 (Monte Carlo Methods)


Is "to drape a medal" correct usage?

Question: I am trying to describe the act of an official attaching a medal to a recipient's clothing (chest) during an awards ceremony.  Is "to drape a medal" the correct usage?  I don't think "to pin a medal" sounds formal.
Comment: Well, if it's not on a ribbon or sash then you're not draping it.  "Pin on" is perfectly correct, though you could always wimp out and just say "award".
Comment: @HotLicks Yes, I did think about "award" and "bestow" and felt much like you said that it was wimping out!
Answer: I don't believe to pin and to drape differ at all in terms of register or formality. The difference is semantic:

pin (v): attach or fasten with a pin or pins in a specified position.
drape (v): arrange (cloth or clothing) loosely or casually on or around something.

You may find examples of "drape a medal around someone's neck," but the action you want to describe - "attaching a medal to a recipient's clothing (chest) during an awards ceremony" - is clearly one of pinning, not draping.
As a side note, we do have the following expression in English, which is a caustic way of responding to someone's boasting:

Would you like a medal or a chest to pin it on?
Comment: RT, thank you.  By the way, I don't quite understand the expression; by implying that the person who is boasting has no chest, does it try to denigrate that person as less than human? Just curious.
Comment: I don't think most people interpret the expression too deeply; rather, they simply understand the idea of "don't be such a braggart." But I've seen different explanations of the "chest" part of the expression; some say it implies the person should be more "manly", others that it relates somehow to "puffing out one's chest", which is another way of saying "boasting." I honestly don't know, but there is no strong implication that the person doesn't have a chest.
Answer: This is just me talking from 30 years as a florist... (seen a lot of funerals) The only time I've heard "drape" a medal, is when someone puts it on a dead body lying in state, or on the casket. (Or, on a likeness of the recipient.) I don't think you use "pin" or "award" in the case of actually presenting it posthumously.

Is "to drape a medal" correct usage?


Why are acid-base reactions so exothermic?

Question: If I mix sulfuric acid with sodium hydroxide, the solution really heats up. Could someone explain why acid-base reactions are exothermic from a molecular perspective?
Comment: When an acid meets a base in a beaker... How easy is it to find a strong acid or base in nature? It isn't - it is hard work to make them. Well, all that work comes out when you mix them back together again. Write out the reactions and see what happens.
Comment: Sorry if this is too basic, but imagine you ripped a bunch of water molecules in two, throwing the H+ pieces in 1 jar and the OH- pieces in another. All the energy put into that comes crashing back at you when you mix the solutions together, allowing the oppositely charged pieces of water to come back together again. No matter the path actually taken to get to this state of separated water molecules (H+ in the strong acid, OH- in the strong base), that's the energy that you get back in the form of heat when you mix the two. Is that what you're shooting for when you say "molecular" perspective?
Comment: Sodium hydroxide and Sulphuric acid have $-\Delta_fH^\circ$ around $\pu{1300 kJ/mol}$ and sodium sulfate and water have around $\pu{1500 kJ/mol}$. So we have an exothermic reaction.
Answer: One can think of it as simply because of electrostatic attraction. Basically, an acid produces $\ce{H+}$ ions in water while a base produces $\ce{OH-}$ ions in water. So when you mix an acid and a base (e.g. sulfuric acid and sodium hydroxide) in a beaker, you get a solution containing $\ce{H+}$ and $\ce{OH-}$ ions. So, when these ions are far apart, there exists potential energy between them (because opposite charges attract each and want to come closer together). So when these ions come closer together, the attraction between them becomes strong enough that a bond forms between the ions to form $\ce{H2O}$. During this process, the initial potential energy between the ions decreases and is converted to heat energy. Hence this is why it is exothermic.
So generally speaking, energy is released when a bond is formed, while energy is required (energy is absorbed) to break a bond. So in the case of acid and base reactions, no bond is being broken, bonds are only being formed. So it must be an exothermic reaction then.
Answer: For a simple answer, an acid, likes do donate its $\ce{H+}$ ions, and a base likes to give off its $\ce{OH-}$ ions. The bond enthalpy of the A-H and B-OH bonds are low. Now the $\ce{H+ and OH-}$ fuse to form a water molecule, giving rise to new bonds, hence is an exothermic process.
Answer: From a purely enthalpic point of view , $H^+$ when combines with $OH^-$ it gives a  water molecule, that is a well known stable molecule. Since the energy must be conserved, when you "becker system" gains energy via the condensation reaction just named, the surrounding must loose energy: this happens since it is heated up by this exothermic reaction. Therefore you can think of the exothermicity as a consequence of the conservation of energy.
Comment: This doesn't explain why acid-base reactions are exothermic, except a small hint that water is stable. Therefore a comment and an NAA