Is ebola non-contagious until symptoms appear? Why?

Question: There's been a lot of talk lately about the man who recently came down with ebola in Dallas, Texas. While I live elsewhere, I keep hearing quotes from CDC and state officials that ebola is not contagious until a person shows symptoms. This is generally used in the context of "Don't worry too much; we have the situation under control." Is this true in all cases? Why?
Answer: First, confirmation from the World Health Organisation:

The incubation period, that is, the time interval from infection with the virus to onset of symptoms is 2 to 21 days. Humans are not infectious until they develop symptoms.

But

People remain infectious as long as their blood and body fluids, including semen and breast milk, contain the virus. Men who have recovered from the disease can still transmit the virus through their semen for up to 7 weeks after recovery from illness.

They also state that deceased people may still transmit the virus via body fluids.
As to why the patients become infectious only when symptoms show, there are several related ideas.  For example, from the CDC:

Ebola virus enters the patient through mucous membranes, breaks in the skin, or parenterally and infects many cell types, including monocytes, macrophages, dendritic cells, endothelial cells, fibroblasts, hepatocytes, adrenal cortical cells and epithelial cells. The incubation period may be related to the infection route (i.e., 6 days for injection versus 10 days for contact). Ebola virus migrates from the initial infection site to regional lymph nodes and subsequently to the liver, spleen and adrenal gland.

According to Dr. Ray Schilling:

Ebola virus disease has an incubation time of 8 to 10 days where the person may complain of some tiredness, but is not sick yet. This is the time when the Ebola virus multiplies. It  paralyzes the immune system and distributes itself through the organ system.

From there, the symptoms and effects of Ebola are fast, according to the article "Ebola Virus Pathogenesis: Implications for Vaccines and Therapies" (Sullivan et al. 2003):

Ebola virus replicates at an unusually high rate that overwhelms the protein synthesis apparatus of infected cells and host immune defenses
Answer: Every infectous disease works this way: if you had contact with x particles (virus, bacteria, etc...), then you have y% chance to get infected (depends on your immune system, luck, etc...), so it has a distribution. This is called virulence, and it can be measured with ID50 (infectious dose by 50% of subjects) and LD50 (lethal dose by 50% of subjects) values. According to animal studies the LD50 is very low by ebola, so it is highly virulent, but it highly depends on the mode of transmission. So this virulency is compensated by low transmissibility: people infected with ebola, but not showing symptoms release too small amount (or nothing) of the virus to infect others. By hemorrhagic fever you bleed out of every hole of your body, and that blood contains a lot of viruses, that's when it can infect others. So this is not a <code>"Don't worry too much; we have the situation under control."</code> case, it works this way currently. This can probably change due to mutations.

Symptoms usually begin with a sudden influenza-like stage
  characterized by feeling tired, fever, pain in the muscles and joints,
  headache, and sore throat.1[12][13] The fever is usually greater
  than 38.3 °C (100.9 °F).[14]
This is often followed by: vomiting, diarrhea and abdominal pain.[13]
  Shortness of breath and chest pain may occur next along with swelling,
  headaches and confusion.[13] In about half of cases the skin may
  develop a maculopapular rash (a flat red area covered with small
  bumps).[14]
In some cases, internal and external bleeding may occur.1 This
  typically begins five to seven days after first symptoms.[15] All
  people show some decreased blood clotting.[14] Bleeding from mucous
  membranes or from sites of needle punctures is reported in 40–50% of
  cases.[16] This may result in the vomiting of blood, coughing up of
  blood, or blood in stool.[17] Bleeding into the skin may create
  petechiae, purpura, ecchymoses, or hematomas (especially around needle
  injection sites).[18] There may also be bleeding into the whites of
  the eyes. Heavy bleeding is uncommon and if it occurs is usually
  within the gastrointestinal tract.[14][19]
Recovery may begin between 7 and 14 days after the start of
  symptoms.[13] Death, if it occurs, is typically 6 to 16 days from the
  start of symptoms and is often due to low blood pressure from fluid
  loss.2 In general, the development of bleeding often indicates a
  worse outcome and this blood loss can result in death.[12] People are
  often in a coma near the end of life.[13] Those who survive often have
  ongoing muscle and joint pain, liver inflammation, and decreased
  hearing among other difficulties.[13]
The time between exposure to the virus and the development of symptoms
  of the disease is usually 2 to 21 days.1[10] Estimates based on
  mathematical models predict that around 5% of cases may take greater
  than 21 days to develop.[11]

wikipedia - Ebola virus disease

The LD50 of mouse-adapted EBO-Z virus inoculated into the peritoneal
  cavity was ~1 virion. Mice were resistant to large doses of the same
  virus inoculated subcutaneously, intradermally, or intramuscularly.
  Mice injected peripherally with mouse-adapted or intraperitoneally
  with non-adapted EBO-Z virus resisted subsequent challenge with
  mouse-adapted virus.

1998 - A Mouse Model for Evaluation of Prophylaxis and Therapy of Ebola Hemorrhagic Fever

Although outbreaks of Ebola virus have largely been confined to
  endemic regions, their high fatality rate, ability to transmit
  person-to-person, and low lethal infectious dose make Ebola virus a
  dangerous threat to public health and pose a great risk for
  researchers working with these viruses as well as health care
  personnel treating patients during outbreaks. Furthermore, their
  potential to be developed into aerosolized biological weapons also
  causes grave concern for their use as a bioterrorism agent ( Bray,
  2003).

2008 - Protection against lethal challenge by Ebola virus-like particles produced in insect cells

Some interesting story about the topic (others were not so lucky):

In 2004, a virologist at USAMRIID was working in a BSL-4 laboratory
  with mice that had been infected 2 days before with a mouse-adapted
  variant of the Zaire species of Ebola virus (ZEBOV) (2). The virulence
  and infectious dose of this variant of ZEBOV are unknown in humans;
  wild-type virus has a case-fatality rate of up to 90% (3).
The person had been following standard procedure, holding the mice
  while injecting them intraperitoneally with an immune globulin
  preparation. While the person was injecting the fifth mouse with a
  hypodermic syringe that had been used on previous mice, the animal
  kicked the syringe, causing the needle to pierce the person's
  left-hand gloves, resulting in a small laceration. The virologist
  immediately squeezed the site to force the extravasation of blood.
  After decontamination of the blue suit in the chemical shower, the
  injured site was irrigated with 1 liter of sterile water and then
  scrubbed with povidone-iodine for 10 minutes.
In terms of exposure risk, the needle was presumed to be contaminated
  with virus-laden blood, although it was suspected that low levels of
  virus were present on the needle. The animals had not yet manifested
  signs of infection, and much contamination may have been removed
  mechanically when the needle pierced the gloves. The local
  decontamination of the site also reduced potential for infection.
USAMRIID medical, scientific, and executive staff concluded that the
  person with potential exposure warranted quarantine in the MCS.
  Contact plus airborne precautions (gown, gloves, N95 mask, eye
  protection) were used, with a plan to upgrade to BSL-4 precautions for
  signs or symptoms of illness. These extra precautions were instituted
  while the patient was asymptomatic for several reasons: 1) the timing
  of initial clinical manifestations with regard to potential for
  shedding virus were not known for this specific isolate in human
  infection; 2) there was interest in ensuring all infection control
  procedures were being followed appropriately in advance of clinical
  illness; and 3) there was interest in reducing any potential
  confounders, such as a caregiver transmitting a febrile respiratory
  infection to the patient, which might lead to unnecessary procedures
  or additional isolation. The person was monitored for routine vital
  signs; daily laboratory studies (coagulation studies, blood counts,
  chemistries, viral isolation, D-dimer) and regular physician
  assessments were performed.
Over the next several days, discussions were held with several
  internationally recognized filovirus experts regarding potential
  treatments or postexposure prophylaxis options. Local and state public
  health officials were also notified. The consensus opinion was that
  there was no safe, readily available source of immune plasma and
  little evidence existed to support its use. Emergency investigational
  new drug (IND) protocols were established for treatment with
  recombinant nematode protein (rNAPc2) and antisense oligomers, with
  the intention to consider implementation only if the patient
  demonstrated evidence of infection.
Ultimately, none of the 5 mice had confirmed viremia at the time of
  the incident. The patient did not become ill or seroconvert and was
  discharged after 21 days.

2008 - Managing Potential Laboratory Exposure to Ebola Virus by Using a Patient Biocontainment Care Unit


Dynamically creating components vs Using Aura:if

Question: Could someone please enlighten me on the pros and cons and use-cases of creating components dynamically from JavaScript as compared to using Aura:if in the markup to render components? I am not quite sure I understand when to use one or the other.
Answer: AFAIK, dynamically creating components was tricky and difficult to debug. This is why LWC's approach to disabling this feature seems to show that SF is shying away from usage of modals created by dynamically created components and removing other features like two way binding.
About your question, it depends on what you are trying to do. If you are trying to show/hide components based on minimal requirements you can use CSS, aura:if or you can use <code>$A.createComponent()</code>. A particular use case for creating components would be when you need to show large amounts of data and only when it's necessary.
Comment: I did not know that SF is trying to move away from the dynamic creation of components going forward. This is definitely significant.
Answer: My 2cents:
One of the use cases is  if you have a backend metadata framework and you load the component to load on the screen from there in run-time.
Basically you wont know what component you need to load till run time. In such cases you would need dynamically created components. I had asked same question for LWC before
If you have like 5 stepped process and you know what components to render but just that based on certain information the step will get inferred in run-time then you would use aura:if to load corresponding step's component.
Comment: Loading components from the back-end metadata framework in run-time using aura:if is possible but the markup will end up being verbose and hard to understand if there are numerous components, right?
Comment: @user73893 , but if its run-time the markup will just contain facets and even more difficult to understand since the components are loaded in javascript, so its better to use aura ifs that way developers can clearly see the components that are getting rendered


How to set a time limit for VPN users?

Question: I've been commissioned by my boss to set up a lab for our customers that they can access via VPN. Each customers should have access to the lab for either 80 or 100 hours, depending on what they purchase. How can I do that? Is there a way to keep track of the time a user is connected via VPN and then close that connection once he or she reaches the time limit?
Comment: Wow. Not a single technical detail in your question. How are we supposed to provide you an answer?
Comment: If I haven't been given any technical details, I don't see how I can share any with you.
Answer: The specific answer will depend on your specific VPN software but, in general, yes. Most VPN software supports the use of RADIUS for AAA (authentication, authorization, and accounting). In this case what you want is RADIUS authentication and accounting data so that when a user logs on and logs off the VPN you can collect those start/stop times. Your VPN solution should also use RADIUS for authentication so that you can deactivate an account after some usage amount (tracked be the accounting part) has been exceeded.
This is probably not going to all be built into your VPN solution but the foundation for it should be there if RADIUS is supported for AAA. You will probably either need to write or find a backend application which can track RADIUS start-stop accounting messages and enable/disable authentication for a user based on the amount of time which was used.
Comment: Thank you for the answer. Now, I think I know how to set up what my boss asked me.

How to set a time limit for VPN users?


How to restrict category creation to admins only while allowing editors to still pick category

Question: Is there a hook which would enable an admin to disallow editors and authors from creating new categories for posts?  Only admins should be able to create new categories.  Editors & authors need to pick from what they're given.
Answer: This has to do with the capabilities tied to the current user role.
In your case you are looking for manage_categories capability.
Option 1)
Install a Plugin, which enables you to edit the capabilites (Just "Members", best plugin for that in my opinion, or "user role editor".)
Option 2)
WordPress has this separation already build in.
"Editors" can manage categories.
"Authors" can not!
So, you only would have to give the users the "Author" role that should be enough to restrict it.
Option 3)
Do it via code in your functions.php with something like:
<code><?php

    global $pagenow, $typenow;

    if(($pagenow === 'edit-tags.php') && $typenow === 'taxonomy') {
        if(!current_user_can('manage_categories')) {
            // Do whatever you want them to see.. redirect to home or whatever
            return false;
        }
    }
</code>
I havent' tested the code above, but that should be the direction to go.
Comment: Thank you. I knew authors don't have the ability so maybe play it safe with out an extra plugin and bump everyone down a notch


Extracting statistics from raster within extent of a polygon using ArcMap

Question: I have a polygon representing the extent of a study area. This polygon is overlaid to a raster representing the quality of land, which is classified into 5 classes (from bad [1] to good [5]). I would like to have ArcMap (10.1, advanced license) calculate how much land within the polygon is bad, how much is mediocre, and so on.
How can I accomplish this?
Comment: Maybe I find the answer myself. I can clip the raster to the extent of the polygon, and then open the raster attribute table and calculate how many pixels fall in each quality class.
Answer: You may use Zonal Histogram. As Input raster of feature zone data, specify your polygon(s). As Input value raster, the land quality raster. The output table will show each land quality class as a row, each polygon class as a column. Thus if you have more than one polygon, you may want to group them into classes beforehand, using a unique value for each class in a special column. This column is specified as the Zone field in the tool. An alternative is to select only the polygon you are interested in and only then run the tool.
Comment: Thought as much, manually I would Clip, turn the raster to points, Join with polygon and Summarize.
Comment: Thank you for your useful reply. My solution led essentially to the same thing, but it was a little more tricky.


Mining 0 fee transactions

Question: If a miner is payed per block found, why not scrape the bottom of the barrel and full up blocks with 0 fee transactions? You would still be getting coins for blocks found just not the fees. The bonus would be no competition on finding blocks. Win/win for everyone...
Answer: Because fees + 12.5 BTC > 0 + 12.5 BTC. It is a lose for the miner because they could have picked transactions that would have paid them more.
Answer: I think you are assuming that miners who are picking low fees transactions are not competing with anyone which is incorrect. Mining is not progressive(i.e your chances do not increase the more you try), it is independent chance of success for every try. You still have the same chance to find a new block, regardless of the transactions you pick. So, there is no bonus advantage.
Therefore, it is always useful to pick high fee transactions than the low fee ones.
Answer: You seem to be under the false impression that miners create blocks based on approving the most transactions the fastest. So you've concluded it would make sense to just fill up the block with zero fee transactions and claim the block reward. It doesn't work like that at all.
Miners solve a block via a cryptographic process that has nothing to do with confirming transactions. They get the same reward at the same likelihood despite what transactions they choose to approve. Solving the blocks is part of the game theory that makes bitcoin work as an autonomous and trustless entity. It is called "proof of work" and ultimately allows miners who didn't solve the block to take at face value the word of the miner that did.
Please see What is mining? That resource should clear up where transaction processing and block solving begin and end.
Because block solving and transaction processing are not connected, transaction fees are subject to classic supply and demand laws. Users decide what fee to send, so miners will pick the higher fees first.
Your confusion may also come from the fact that blocks do have a size limit, which translates to an average transactions per second limit. If there were no transactions, miners would still solve blocks and report only the coinbase transaction, the one that generates the reward bitcoins. This is because the miner found the hash, not that they filled up the block.

Mining 0 fee transactions