one - way hash chains are an important cryptographic primitive and have been used as a building block of a variety of cryptographic applications such as access control , one - time signature , electronic payment , on - line auction , etc .in particular , there are many micropayment schemes based on one - way hash chains , including payword , netcard , micro - ikp and others .  by definition ,micropayments are electronic payments of low value .other schemes designed for payments of high value normally use a digital signature to authenticate every payment made .such an approach is not suitable for micropayments because of high computational cost and bank processing cost in comparison with the value of payment .the use of hash chains in micropayment schemes allows minimizing the use of digital signature , whose computation is far slower than the computation of a hash function ( according to , hash functions are about 100 times faster than rsa signature verification , and about 10,000 times faster than rsa signature generation ) .moreover , because a whole hash chain is authenticated by a single digital signature on the root of chain , successive micropayments can be aggregated into a single larger payment , thus reducing bank processing cost .there are a variety of improvements to hash chains .for example , in the paytree payment scheme , jutla and yung generalized the hash chain to a hash tree .this construction allows the customer to use parts of a tree to pay different vendors .recently , researchers have proposed a number of improved hash chains , which are more efficient in terms of computational overhead and storage requirement .this paper is organized as follows . in section [ mdhc ]we introduce the notion of multi - dimensional hash chains ( mdhc for short ) .we also analyze efficiency of this construction and show that rsa modular exponentiations could be used as one - way hash functions of a mdhc .section [ cashlikeschemes ] describes two cash - like micropayment schemes based on mdhc , which have a number of advantages in terms of efficiency and security . in section [ improvepayword ]we also examine some possible improvements to payword and similar schemes . finally , section [ conclusion ] concludes the paper .the notion of mdhc originates from one - way hash chains and one - way accumulators .here we briefly describe these two constructions .a hash chain is generated by applying a hash function multiple times .suppose that we have a one - way hash function and some starting value .a hash chain consists of values where for .the value is called the root of hash chain .the figure below depicts a hash chain of size :  in contrast , a one - way accumulator is the output of multiple hash functions , each of them applied only once :   in order to ensure that the output is uniquely determined regardless of the application order , functions must be in pairs commutative , i.e. for any .  combining the two constructions described above , we define a multi - dimensional hash chain as the result of multiple applications of different commutative hash functions , so the root of an -dimensional hash chain is :   it is necessary to note that mdhc differs from other generalizations of normal hash chain such as hash tree , which is used in paytree scheme . in particular such treesare generated from multiple leaf nodes , while a mdhc is generated from a single starting value ( i.e. the value above ) .we begin with necessary definitions .  *_ definition 1 ._ * two functions are called commutative if for any .* _ definition 2 ._ * a one - way function is called one - way independent of one - way functions of the same domain if for any , computing is intractable even if values are known .and now we define mdhc as follows .  * _ definition 3 . _ * let be one - way hash functions that are in pairs commutative and every of them is one - way independent from all others .an -dimensional hash chain of size consists of values where :   the value is called the starting node , and the value is called the root of the mdhc , which is uniquely determined from due to commutativity of hash functions :   as an illustration , the figure below depicts a two - dimensional hash chain of size ( 3,2 ) :   in recent literature , there are a number of improvements to one - way hash chains that aim to be more efficient in terms of computational overhead and storage requirement .a widely used metric for one - way hash chain efficiency is the storage - computational complexity , which is the product of the traversal overhead and the storage required to compute consecutive nodes of the hash chain .it is easy to see that a linear hash chain size of has storage - computational complexity of .in fact , if we precompute and store all nodes ( storage of , then no computation is needed when a node is requested ( traversal of .alternatively , we can store only the starting value , and compute every node from the beginning each time it is requested .this approach requires storage of and computations .also , if we store each of nodes , then storage of and computations are required .so , in any case , the storage - computational complexity of the linear hash chain is .in the authors have proposed new techniques that make traversal and storage more efficient , which require computations and storage , resulting in storage - computational complexity of .recently , hu et al . have presented a new hierarchical construction for one - way hash chains that requires storage and only traversal overhead .  in our case of -dimensional hash chain of size ( for simplicity we assume all dimensions have the same size ,the number of nodes is .if we store only the starting node of the chain ( storage of then maximal number of calculations required to compute any node is , or if we select . in that casethe storage - computational complexity of mdhc is , which is equivalent to the results in .the advantage of mdhc is its simple implementation that does not rely on the so - called pebbling technique , which is used in the constructions mentioned above .however , the main limitation of this construction is the fact that hash functions have to meet the conditions described in the definition of mdhc .the rsa modular exponentiation is known to meet these conditions , but it is not as fast as the traditional hash functions , e.g. md5 or sha .let consider the function of rsa modular exponentiation : where is some constant value and is an rsa modulus , which is a product of two large primes of equal bit length and .  according to , the rsa modular exponentiation functions with appropriately selected exponents could meet mdhc requirements .first , obviously these functions are in pairs commutative :   second , one - wayness of these functions is derived from the rsa assumption , which states that the problem of finding the modular root is intractable .  finally , regarding one - way independence of functions , shamir showed that if is not a divisor of the product then the modular roots are insufficient to compute the value of .therefore we can use the functions of rsa modular exponentiation as one - way hash functions to construct multi - dimensional hash chains .  in that casewe have following recursive expression : where are exponents of rsa functions respectively .note that if one knows the factorization of ( i.e. knows and , then one can compute quickly by using following expression : where , and denotes the euler s totient function .the expression above consists of only one modular exponentiation with modulus and modular multiplications with modulus .since a multiplication is far faster than an exponentiation , this expression allows us to compute from in a very effective manner .cash - like payment schemes use the notion of electronic coin , which is an authenticated ( by the bank ) bit string that is easy to verify , but hard to forge .examples of such coin are hash collisions ( as in micromint ) , or digital signatures ( as in ecash ) .let s recall the definition of mdhc .if we select the size of the hash chain with then all nodes ( with all , except have the same hash value : .so we can use a pair as an electronic coin since :  * it is easy to verify by just one hashing . *it is hard to forge because hash functions are one - way , and their one - way independence assures that coin forgery is impossible even if one knows other coins with the same root .as a proof of that concept , we suggest two micropayment schemes based on mdhc with the rsa modular exponentiation . we refer to these as s1 and s2 schemes .we assume that there are three parties involved in a micropayment scheme , namely a bank ( b ) , a customer ( c ) and a vendor ( v ) .b is trusted by both c and v.  setup :  * b selects an rsa modulus where and are large _ safe _ primes of equal bit length .a prime p is called safe if where is also an odd prime . *b chooses constant values that satisfy the condition of one - way independence , i.e. each is not a factor of .these values together with modulus are public parameters and can be used for multiple coin generations . * to generate coins, b picks a random value and computes :  + now b has coins . *b keeps in a public list of coin roots .* for prevention of double - spending b keeps another list of all unspent coins .in addition , b can also generate vendor - specific as well as customer - specific coins by using some bit portions of constants to form vendor i d and customer i d , similar to the technique used in micromint scheme . * c buys a sufficiently large number of coins from b before making purchases .  payment :  * c pays a coin to vendor v. * v verifies the coin by computing , and checks if is in the list of coin roots . note that this list is relative small and does not changefrequently so c could keep it locally . * to assure that a coin was not double - spent , v either checks the list of unspent coins on - line with b , or checks ( off - line ) the list of coins he already received if the coin is vendor - specific .redemption :  * v deposits the coins he got from customers to b and receives an amount corresponding to number of coins .  at the end of the coin validity period ,c can sell unused coins back to b or exchange them for new coins .the proposed above scheme has several advantages :  * coins are hard to forge under the rsa assumption .* payment can be made off - line by using vendor - specific coins . *if customer - specific coins are not used , the scheme is anonymous and untraceable because coins contain no customer information and there are no links between coins .however , the disadvantages of this scheme are :  * generation and verification of coins is not very efficient .each coin requires one modular exponentiation to generate or verify it , which is much slower than normal hash calculation .* the list of unspent coins can be very big , though this is a common problem of most coin - based schemes .  to overcome these disadvantages , we propose a modified scheme with larger size hash chains ( i.e. with .in this scheme , b generates chains of coins at once , rather than single coins .each coin chain is similar to the hash chain used in the payword scheme .setup :  * b selects public parameters and in the same way as in the s1 scheme .let be the size of the hash chains ( for simplicity we assume all dimensions have the same size i.e. .* b picks a random value and computes :  + now b has coin chains .each of those chains contains exactly coins for where : +  + the coins from one coin chain must be paid to the same vendor . * for double - spending prevention , now there is no need to keep track of all unspent coins .instead , b keeps the list of first coins of all unused chains . * as in the s1 scheme , coin chains can be vendor - specific as well as customer - specific .* c buys coin chains from b before making purchases .payment :  * c pays a vendor v the coins from a coin chain . the first coin of the chain is verified by computing and lookup of in the list of chain roots .it is also checked for double - spending by lookup in the list of unused chains .any subsequent coin is verified by checking that it hashes to the previous coin in the chain , as in the payword scheme :   redemption :  * v deposits the last coin ( i.e. the coin with highest index of each coin chain he got from customers to b and receives an amount corresponding to number of coins .  comparing with the s1 scheme ,this modified scheme retains all advantages of s1 , but storage requirement is reduced by factor of .in fact , b keeps track of only the first coins of -coin chains .another advantage of this scheme is more efficient coin generation .because b knows the factorization of m , he can compute the starting node of a coin chain by just one modular exponentiation .thus the cost of this computational expensive operation is shared over all coins of the chain .similarly , b can also verify coin chains that he got from vendors by computing one modular exponentiation per chain .generally speaking , the s2 scheme combines the advantages of two approaches .a first approach uses unrelated coins that are convenient for payments to multiple vendors .another approach uses chains of coins that are easy to generate and verify . in our scheme different coin chainsare unrelated , while coins within a chain are generated and verified only by repeated hashing .the payword scheme has been proposed in .it is based on one - way hash chains described in the section [ mdhc ] . in this scheme , before making purchases a customer c generates a hash chain ( that is a chain of paywords ) and sends his signature of the root to the vendor v. the customer then makes a payment to v by revealing the next payword , which can be verified by checking that it hashes to the previous payword .the payword scheme allows a vendor to aggregate successive payments from a customer by sending only last payword he got from the customer to the bank for redemption .however , a vendor can not aggregate payments of different customers , nor can a customer use the same chain of paywords to make payments to different vendors , because there is no way to merge different hash chains .  by using mdhc , we can improve payword scheme in a number of ways .below we briefly describe two of such possible improvements .note that some irrelevant details in these descriptions are omitted for convenience .in the original payword scheme the size of the hash chain must be large enough .for example , if each micropayment is worth 1 cent and total payment is up to $ 100 , then a chain with size of 10,000 must be generated , which requires 10,000 hash calculations .we can reduce the number of hash calculations by using mdhc instead of linear hash chain .the idea is that every dimension of mdhc will be associated with different weight ( or denomination ) according to some number system ( e.g. decimal or binary ) .suppose we have an -dimensional hash chain with size of .if one step in the ( + 1) dimension is equivalent to steps in dimension , then a node corresponds to the value :   the maximal value that could be represented by this hash chain is and the number of hash calculations required to generate the hash chain is . in the case of a binary number system ( i.e. it is .  returning to the example above , the hash chain now requires just 14 calculations to generate .  similarly ,verification of the payword also requires significantly less calculations than in the case of the original payword scheme .   in the payword schemea hash chain can be used for payments to only one vendor .a customer must generate different hash chains for payment to different vendors .we can overcome this drawback by using mdhc as well .let every vendor in the payment system is assigned a different hash function ( i.e. a public parameter in the case of rsa modular exponentiation ) .now , in order to make payment to different vendors , a customer generates an -dimensional hash chain with their public parameters and signs its root .the customer then makes a payment to by revealing the next payword in the dimension , starting from the root of hash chain .in particular , if the current payword is , the next payword in dimension will be .  at the end of the day, vendors deposit the last paywords they got to the bank for redemption .the bank picks the last payword ( which is the one with highest indices ) among paywords with certain root ( which all come from one customer ) .finally , the bank credits vendors by the amount equivalent to , and debits the customer s account accordingly .  there could be other possible improvements to the payword scheme by using mdhc .for example we can aggregate payments of different customers into a single mdhc that is generated by the bank , or we can construct a payment scheme with multiple currencies , etc .the proposed multi - dimensional hash chain is a simple and efficient construction for one - way hash chains .whereas a traditional one - way hash chain has a storage - computational complexity of , our construction achieves a complexity of , which is comparable with the best result among other recently proposed constructions .we show that multi - dimensional hash chains can be very useful in micropayment schemes .in particular , we suggest two cash - like micropayment schemes based on mdhc with rsa modular exponentiation as one - way hash function .the first scheme utilizes coins that are hard to forge under the rsa assumption. this scheme could be also off - line and untraceable .the second scheme has additional advantages including very efficient coin generation / verification and much less storage requirements .we also point out some possible improvements to payword and similar schemes by using mdhc , including payword chains with multiple denominations , and a scheme that allows payment to multiple vendors using the same payword chain .r. anderson , h. manifavas , and c. sutherland .netcard - a practical electronic cash system . _ proceedings of the 4th security protocols international workshop ( security protocols ) _ , pp.4957 , lecture notes in computer science vol .springer - verlag , berlin , 1996 .r. rivest and a. shamir .payword and micromint : two simple micropayment schemes . _proceedings of the 4th security protocols international workshop ( security protocols ) _ , pp.6987 , lecture notes in computer science vol . 1189 .springer - verlag , berlin , 1996 .b. schoenmakers .security aspects of the ecash payment system . _ state of the art in applied cryptography : course on computer security and industrial cryptography - revised lectures _ , pp.33852 , lecture notes in computer science vol .springer - verlag , berlin , 1998 .

Abstract: one - way hash chains have been used in many micropayment schemes due to their simplicity and efficiency . in this paper we introduce the notion of multi - dimensional hash chains , which is a new generalization of traditional one - way hash chains . we show that this construction has storage - computational complexity of per chain element , which is comparable with the best result reported in recent literature . based on multi - dimensional hash chains , we then propose two cash - like micropayment schemes , which have a number of advantages in terms of efficiency and security . we also point out some possible improvements to payword and similar schemes by using multi - dimensional hash chains .


field emitters such as carbon nanofibers play an important role in today s vacuum electronics. they are also used in ion sources , for example field ionization sources for neutron generators . in all cases , it is important to be able to characterize the field emitter samples , which can be done using electron field emission experiments , see for example ref . .electron field emission occurs as a result of a tunneling process of electrons through a potential barrier .this was first reported by fowler and nordheim in 1928, who derived an equation for the emitted current . in their 1-dimensional model ,the emission current is expressed as a function of the local field , the emitter area , and the work function of the material . since then, the model has been extended to include a number of correction factors.  the fowler - nordheim ( fn ) equation can be rewritten using a different set of variables , such that the relationship between these new variables is linear .the linear fit results in two parameters : the slope and the intercept . if one acquires several fn - plots for the same sample or for a set of different samples , different slope - intercept data points are obtained .when plotting the slope against the intercept , an almost linear relationship has been observed in many cases . it has not been clear what the origin of this linear relationship is or what it implies . in this paper ,the linearity is explained using a statistical model simulating field emission from tips with a random distribution of height , radius , and work function .in the following , the equations used for the simulations presented in this paper are introduced . for an introduction into the theory of field emission ,the reader is referred to gomer , and for a short summary to the article on fn - analysis by forbes _ _et al.__  the simplest equation for fn - tunneling is given by   where is the emitted current , and are the so - called first and second fn - constants , is the emitting area , is the work function of the material , and is the local electric field .the values for the fn - constants are {a  ev}{v^2} ] , with , , being the charge and mass of an electron , respectively , and being the reduced planck constant .the local field can be expressed using the applied field and a local field enhancement factor , as   equation  is derived for the 1-dimensional case and a uniform applied field . in experiments ,the field is enhanced at a step or a sharp point . the enhancement factor directly expresses the amount of enhancement from a tip - like structure compared to a flat surface . for cylindrical tips ,a simple estimate is given by where is the height of the tip and the radius .a more precise estimate is given by edgcombe and valdr as ^{0.9}.\ ] ] if there are many emitters in an array structure , there is also a shielding effect that needs to be taken into account , especially if the tips are very close to each other .the shielding effect can be estimated using ,\ ] ] where is the spacing between the tips .it can be helpful to rescale the fn - equation using where is the schottky constant ( ; is the electric constant ) . by doing this ,the fn - equation now depends on a dimensionless variable . using this rescaling approach and adding some correction factors , the fn - equation can be written as \frac{1}{f}\right).\ ] ] this equation is physically more realistic than eq ., since it takes image forces into account .this has the effect that the tunneling barrier is lower compared to the case in eq . , and higher emission currents ( typically by a factor of 100 or more )are predicted .the linear relationship of the fn - plot is seen when rewriting eq .  as clearly , this equation has the linear form , more realistic equations , such as equation , generate nearly ( but not exactly ) linear fn - plots .these more realistic theoretical plots , and also many experimental fn - plots , can in practice be fitted by a linear equation of form eq . .in all the figures in this paper , the quantity is expressed in the units ( ) before the natural logarithm is taken .  from the slope and the intercept of the fit , one can calculate two of the three parameters , , and , if one makes an assumption about the third parameter .often one assumes a known value for the work function in order to extract the other two parameters . due to the form of the equation , it is not easy to obtain information on the work function and the field enhancement factor at the same time , since they appear almost as , which makes them difficult to distinguish. furthermore , it is non - trivial to define the emitting area .this is due to the fact that the original equation was derived for the 1-dimensional case , whereas for a 3-dimensional sharp tip the electric field will not be constant across the surface and there will be a field dependence of the area that is not included in these equations .in addition , time dependence of any of the parameters is not included in this analysis .time dependent effects include changes in the work function and field enhancement factors due to absorbents on the surface or blunting of the tips due to sputtering or heating effects .in order to compare different samples or to examine the behavior of a single sample over time , plotting the slope and intercepts from fitting different fn - plots was introduced. often these plots are also referred to using their japanese names : seppen - katamuki plots or sk - plots for short . from eq . , one can calculate lines of constant work function or constant field enhancement factor for these plots .assuming one of the relationships between radius , height , and field enhancement factors listed above , equations for constant height and constant radius can also be derived.  in sk - plots , a linear relationship between the slope and the intercept is often observed . however , this linear relationship can not easily be explained assuming only a change in a single parameter , such as the radius . for a possible explanation using the simple fn - equation , one needs to assume a more complex radial dependency of the area. another problem with explanations of this kind can be seen if one looks at data from repeated experiments , for example , as shown in figure 7 in the paper of gotoh _ _ et al.__ the data points do not start at one end of the line and then move along to the other end , as one would expect if the change would be due to a continuous function , but rather the distribution of data points along the line appears to be random .the linear relation shown in the sk - plots seems to be orthogonal to a change in work function and therefore different parallel lines in a sk - plot have been attributed to a change in the work function and absolute values have been extracted .a good example of this can be seen in the work of gotoh _et al._, where the authors were able to extract the work functions for different crystal planes of a tungsten emitter .charbonnier , southall , and mackie also investigated further possible explanations for the linear behavior in sk - plots , and considered whether nano - protrusions on top of a single emitter can be the cause .they found that a single protrusion can not fit the experimental data , but if several protrusions are used then good linear fits to the sk - plots can be obtained by choosing the correct parameters for these protrusions .for an array of tips , the fn - equation becomes more complicated , since one has to deal with many tips that will show a distribution of heights , radii and work functions . also , the shielding between tips can not be easily computed , since neighboring tips will have different heights and radii and therefore the shielding effect will vary .the shielding effect can be neglected , however , if the distance between tips is larger than twice the height of the tips. from here on , the assumption is made that the tips on the sample are spaced even further apart and therefore any shielding effect is ignored . to make the model very simple , eqs . are used . the index is used to distinguish different tips , that is , will be the radius of tip , etc .furthermore , a very basic relation for the area of each tip , , is assumed .the total current for a single sample can then be written as   nicolaescu _ et al . _have used a similar equation to directly fit fn - plots using parameters of the distribution as fitting parameters .  the distribution of most parameters is most likely a log - normal distribution ( negative values for height and radius from a normal gaussian distribution would not make sense ) .a log - normal distribution for the radius has also been observed by ding _et al._, as well as by park _et al . _ for the field enhancementin the following , the results of simulations using eq .  with varying parameters are shown . the difference between a simple model and using the more realistic fn - equation , and the different approximations for the field enhancement factorsare also examined .various random distributions are explored ( log - normal , normal , uniform ) , as well as the effect of just using a constant value . when comparing a log - normal / gaussian distribution with a uniform distribution, the range in values for the uniform distribution is chosen to coincide with six standard deviations of the log - normal / gaussian distribution .histograms of example distributions are plotted in fig .[ fig : distributions ] .the simulations were carried out using python. the numerical python module numpy was used for most of the calculations and for random number generation , pylab was used for plotting , scipy was used for the fitting routine , and ipython was utilized to execute the main routine in parallel on a local ipcluster .the basic algorithm consisted of the following steps for calculating samples of size : a ) generate random distributed values for radius , height and work function , and calculate field enhancement factors for each tip ; b ) for a given range of applied electric field , calculate the total current for the sample for each field value ; c ) perform a linear fit on the simulated data using eq .  and save the fit parameters ; d ) repeat steps a)-c ) times to generate statistics ; e ) plot results .  for the following results , the values shown in table [ tab : values ] are used unless otherwise noted .the electric fields used for the fit were 20 evenly spaced values between {v}{\mu  m} ] ..parameters used in the simulation . for a uniform distribution , the minimum and maximum values are taken as and for constant values just the value for is used . [cols="^,^,^,^",options="header " , ]   in figs .[ fig : uniform_r ] and [ fig : sizes ] , results are plotted for a sample with a constant height and a constant work function , but different radial distributions : uniform and log - normal .furthermore , the number of tips per sample , in eq . ,is varied as shown in the plots .one can see that a nearly linear relationship emerges for large and a log - normal distribution of tip radii .this emerging behavior is purely statistical in nature due to the fact that a log - normal distribution has a non - zero probability of containing very sharp tips .however , when one looks more closely at a single sk - plot and generates better statistics , a different picture is revealed .a histogram of a simulation using 128 emitters per sample for a total of 5000 samples is shown in fig .[ fig : zoom ]    and shows that instead of a linear relationship the sk - plot is actually closer to a 2-dimensional gaussian distribution , which would be expected for large numbers . from fig .[ fig : sizes ] , it is clear that the greater the number of tips / sample the narrower the 2-dimensional gaussian distribution will be , resulting in the almost linear appearance .  in fig[ fig : rdist ] , the dependency of the    shape of the sk - plot on the type of radial distribution is explored . obviously ,if only constant values are used , all data points in the sk - plot are the same . a uniform distribution for the radius results in a horizontal distribution of points that only varies slightly on the sk - plot .this is similar to plots of constant radius in previous publications , although using a simpler model for the dependency of the fn - equation on tip radius .a log - normal or gaussian distribution , however , shows an almost linear spread across a wide range of values in the sk - plot , very similar to experimental observations .it is also easy to simulate the effect of the different approximations for the field enhancement factor ( eqs .  ) .the results are shown in fig . [fig : gamma ] .although there is a shift in values , the shape of the resulting plot does not change . therefore , for the purpose of this paperthe use of the simplest approximation is justified .{ \mu m}12 & 12#1212_12%12[1][0] link:\doibase 10.1116/1.4747705 [ * * ,  ( ) ] link:\doibase 10.1038/nature03575 [ * * ,  ( ) ] link:\doibase  10.1016/j.mee.2009.11.036 [ * * ,  ( ) ] link:\doibase  10.1063/1.4802305 [ * * ,  ( ) ] link:\doibase  10.1063/1.3672437 [ * * ,  ( ) ] link:\doibase 10.1116/1.3531929 [ * * ,  ( ) ] link:\doibase  10.1016/j.tsf.2013.02.053 [ * * ,  ( ) ] link:\doibase 10.1098/rspa.1928.0091 [ * * ,  ( ) ] link:\doibase 10.1116/1.4765080 [ * * ,  ( ) ] link:\doibase 10.1116/1.1576764 [ * * ,  ( ) ] link:\doibase 10.1116/1.1760753 [ * * ,  ( ) ] link:\doibase 10.1063/1.2740199 [ * * ,  ( ) ] link:\doibase  10.1116/1.3325835 [ * * ,  ( ) ] link:\doibase 10.1016/0039 - 6028(94)90651 - 3 [ * * ,  ( ) ] link:\doibase 10.1088/0957 - 4484/23/9/095706 [ * * ,  ( ) ] link:\doibase 10.1046/j.1365 - 2818.2001.00890.x [ * * ,  ( ) ] * * ,  ( ) link:\doibase  10.1063/1.1576310 [ * * ,  ( ) ] link:\doibase 10.1116/1.586870 [ * * ,  ( ) ] link:\doibase  10.1143/jjap.35.l1297 [ * * ,  ( ) ] link:\doibase 10.1016/j.apsusc.2007.07.172 [ * * ,  ( ) ] link:\doibase  10.1143/jjap.40.4802 [ * * ,  ( ) ] link:\doibase  10.1116/1.2433950 [ * * ,  ( ) ] link:\doibase 10.1016/s0304 - 3991(01)00117 - 6 [ * * ,  ( ) ] link:\doibase 10.1063/1.1635655 [ * * ,  ( ) ] link:\doibase  10.1116/1.1593641 [ * * ,  ( ) ] link:\doibase  10.1116/1.1689311 [ * * ,  ( ) ] link:\doibase 10.1109/ted.2002.805230 [ * * , ( ) ] link:\doibase  10.1116/1.2184330 [ * * ,  ( ) ] link:\doibase 10.1116/1.2174022 [ * * ,  ( ) ] http://www.python.org [ `` , '' ] ( ) http://www.scipy.org/ [ `` , '' ] ( ) * * ,  ( ) * * ,  ( )

Abstract: in electron field emission experiments , a linear relationship in plots of slope vs. intercept obtained from fowler - nordheim analysis is commonly observed for single tips or tip arrays . by simulating samples with many tips , it is shown here that the observed linear relationship results from the distribution of input parameters , assuming a log - normal distribution for the radius of each tip . typically , a shift from the lower - left to the upper - right of a slope - intercept plot has been correlated with a shift in work function . however , as shown in this paper , the same effect can result from a variation in the number of emitters .


in its present form , scientometrics can not take the place of in - depth science of science .scientometrics does not offer a `` clear window '' into science , but rather something more akin to a stained - glass window , which allows one to gain some impressions of the world , but at the same time imposes its own patterns and colours on that world . in this regard ,the scare quotes around the term `` space of physics journals '' in the title of this paper are intentional  they draw attention to the fact that we must explicitly define what we mean by the term . having refined our empirical insights into the nature of this space , the formal determination may then be used for further scientometric exploration .the history of scientometrics is very interesting in itself , and demonstrates that , in many cases , scientometric understanding of a journal consists in deconstructing the quality of a journal to its bare bones .this suggests that a hard indicator of scientific quality is citation statistics ( we do not go into details , and refer the reader to ) .perhaps the most widely - known and analysed scientometric indicator based on citation statistics is the journal impact factor ( jif for short ) .jif is provided by the journal citations reports ( thomson reuters ) , and is a quantitative measure for ranking and evaluating scientific journals .it consists of `` the average number of citations received per paper published in that journal during the specific period of two preceding years '' .jif is `` a ratio between citations and recent citable items published '' .the jif calculation is well presented in the scientometric literature , therefore we shall not detail it here .jif has become practically the standard measure for evaluating and ranking scientific journals .the receipt of a high jif is an object of fierce competition between scientific publishers ; this indicator is actively used in scientific policy and management .unsurprisingly , jif has been subject to close scrutiny from professional and citizen bibliometricians , as well as scholars , publishers , policymakers and research managers .for example , in 2012 the leading journal _ scientometrics _ published a special edition dedicated to jif , and the journal _ nature _ regularly publishes articles on this subject ( for instance , see ) . since an analysis of the literature on jif is not one of the aims of our work , we refer the reader to several excellent reviews which consider this subject in depth .  despite being the subject of ongoing criticism, jif continues to be widely used .it follows that there must be good reasons for this .it should be recognised that scientometrics has not yet arrived at reflexive analysis over the concept of `` scientific quality of a journal '' ( cf . ) . on the one hand, scientometrics can not regard it as a primitive concept , because it does not belong to the category of observable quantities , and must therefore be a definable concept .but on the other hand , it is impossible to give a precise and explicit definition of the quality of a journal without a more or less comprehensive theory of scientometrics .hence , a satisfactory definition of `` quality of a journal '' can not be anything other than an integral part of the theory of scientometrics .it is difficult to conceive of an operationalisation of the scientific quality of a journal free of scientometric critic .it is clear that this concept expresses a complex social phenomenon .however , whilst setting aside this complexity , in scientometrics it is possible to work with an individual aspect of the concept . in practice ,scientometricians adopt implicit definitions of the scientific quality of a journal when they develop ways to measure scientific recognition , popularity , impact , and so on .the multifaceted nature of the scientific quality of a journal indicates the relatively complex structure of the concept .the differences between the elements of this structure can be so great that this in itself can justify the study of the individual aspects as isolated scientometric constructs .  in light of scientometric practice, it would seem reasonable to consider a scientific journal as a representative of the totality of journals , all coexisting interdependently in the scientific field . to establish the quality of a physics journalit is necessary , _ inter alia _ , to appeal directly to a given class of experimental data . without going beyond the well - established scientometric data and abandoning the search for the _ causa finalis _ of a journal, we can nevertheless aim to find the _ causa efficiens _ of a journal directly , in the space of physics journals ( hereafter spj ) itself .this means that the spj as a system of relations offers the possibility to correlate bibliometric data on journals exclusively among themselves .it is impossible to formulate _ a priori _ concepts about the relations that constitute the spj ; on the contrary , these relations are determined only within the framework of research .thus , the development of theoretical concepts only becomes possible in light of the development of empirical knowledge .the spj , as the product of a distinctive history , generates its own conceptions of the quality of a physics journal .the spj can be interpreted as a system of differences , which manifest themselves as elements of its structure .the spj enables empirical data on journal citation to be systematised within the physics periodicals own inherent system of logic .hence , in order to evaluate the quality of a journal , it is necessary to construct the spj by building on the existing system of differences between journals .  the formulation of the spj as a ( relatively ) autonomous scientometric entity ( i.e. based only on itself ) provides an imperative to uncover the spj through relational concepts . for the present authors ,given the available bibliometric data , these concepts are `` distance between the journals '' and `` situs of a journal '' ( or sj in abbreviated form ) .the sj is defined as the ratio that exists between the properties of a journal , and those of the sample of journals being studied .the sj characterises the structure of citations of a journal relative to a sample of journals . in this paper , the point is not so much the sj of any given journal itself , but rather understanding how sj works .  conceptually , we make six claims about the spj .  1 .we propose that it is a scientometric concept that can encompass both social relations and bibliometric networks , social institutions and scientific resources ( including popularity , scientific recognition , authority , impact , etc . ) .we claim that the spj can be treated as a relational construct , and that can be explained in terms of regularities observed at the level of its constituent relational `` situs '' ( cf .2 .  the concept of the spj is a means of creating an object of scientometric study by constructing synthetic relations between empirical data .however , the spj is the totality of relations , which is not located in the area of scientometric experience in the form of an `` end product '' .this set of relationships is constructed by scientometric theory as a means of studying the systematic connections between empirical data on journals  a tool that brings together bibliometric knowledge into a logical whole .scientometric theory organises not the empirical data themselves , but their statistical representations . by using mathematical concepts , we are able to reduce the gap between scientometric concepts and bibliometric data .we suggest that the spj is inherently non - deterministic .we thus arrived at the probabilistic representation of the spj .4 .  in a scientometric experiment ,almost all that is measured is the probability distribution of citations .this in itself appears to be sufficient justification for identification of the physics journal with the empirical distribution function of citations ( cf .the spj is a bound state of several journals , and therefore consists of a certain number of different stochastic processes . to characterise configurations of such a complex social systemis a difficult problem .but it has a simplifying feature : social relations between scientific journals may be approximated by probability distances between the corresponding probability distributions .the spj is a practical classification of physics journals , which summarises the initial differences between them .this paper aims at contributing to a better theoretical and empirical understanding of the scientific quality of physics journals . in this work ,we first intent to construct and interpret the spj using a bibliometric data set on physics journals extracted from web of science core collection ( wos cc for short ) .the second step is to develop a model of sj .we derive values of sj for physics journals and compare these results with the jif .the data on journal citations and indicators was extracted from the wos cc  scientific citation indexing service , and the journal citation reports  an analytical tool providing bibliometric information about academic journals .both are provided by thomson reuters .the first step was to select all journals included in the `` physics '' category in the journal citation reports , according to the category schema `` essential science indicators '' , which resulted in items .journals which had published less than papers in two years were excluded from the selection , resulting in a narrowed sample of journals .it is worth noting that six of the ten journals with the highest jif were excluded from the sample , since these were review journals publishing a small number of papers per year . taken together , the excluded journals publish on average 55.8 citable items in two years .the next step was to extract information from the wos cc on citations made in 2015 for all papers published in the journal sample during 2013 and 2014 . only `` article '' and `` review '' data types were included in the sample .we opted for a two year publication window , a one year citation window , and `` article '' and `` review '' document types , so that our corpus of would be as close as possible to that which forms the basis for the calculation of jif in the journal citation reports .the dataset was downloaded from wos cc in august 2016 .in addition to citation data , we used journal indicators provided by the journal citation reports for the year 2015 .data on journals publishers and countries were extracted from the `` scopus title list '' .  for statistical data processing , we used the r programming language and ibm spss statistics 22 .in this paper , we treat the word `` model '' approximately as the `` formalism '' , that is , a collection of abstract analytic tools for working formally with bibliometric quantities , deriving formulas , and interpreting them .good formalism is almost as useful as exact formulas .however , a clear grasp of the essence of the sj must be achieved before introducing a formalism itself .there is no reason to justify a formalism which has not been perceived yet .note that in the probabilistic approach , numerical characteristics of a journal are random variables , where the index will sometimes be left out .for definiteness therefore , let us consider the distribution constructed from the sample , for any borel set . in a sense ,the empirical distribution function ( or , in abbreviated form , edf ) , corresponding to the sample , characterizes the journal . to give a scientometric meaning to the edf, we assume that is a property of the state of . this interpretation will serve as a guideline throughout this paper .our key intuition is to think of the sj of as a property of the edf and its relations .we want to evaluate the sj of a given journal in a natural and intuitive way . to achieve our goal of deriving the sj of a journal from first principles ,we represent directly by means of a measurable `` utility function '' .let us suppose , for the sake of argument , that the above - mentioned utility function is a functional  ] of the skorokhod space , comprising all bounded , nondecreasing functions \rightarrow \mathbb{r}_{+} ] ( cf . ) . to help the intuitive interpretation of what follows, we shall treat the space as a phase space .if one adopts this point of view , the state of a journal on is defined by a point .thus , the edf is a point of space , and at the same time possesses an inner structure .let us now be more technical and turn to the derivation of our sj .one knows that is a banach space , and we use and to denote its topological dual and the duality pairing , respectively .this yields that the dual of can be considered as the space of utilities  ] .choose any ; then , the partial order of bishop phelps on can be defined as follows ( cf . ) : \preceq\left[\hat{f}_{y},\hat{f}_{y}^{\star}\right ] \longleftrightarrow \\ & \left\langle \hat{f}_{x}^{\star } , \hat{f}_{x}\right\rangle + \varepsilon\vert \hat{f}_{x } - \hat{f}_{y}\vert_{\infty , d_{b } } \leq\left\langle \hat{f}_{y}^{\star } , \hat{f}_{y}\right\rangle . \end{split}\ ] ] when we interpret the result which we obtain , by mathematical means , in scientometric terms , we obtain information about scientometric enteties . by construction ,the expression is a `` relative gain '' . in the casestudied here , from the formula it can be seen that is a _gain _ of the journal _ relative _ to the journal , with a `` unitary gain '' .( here , we examine two samples and of sizes and , respectively . )more intrinsically , we use in the expression kolmogorov distance of to .it is scientometrically sensible that .trivially , the formula can not , by itself , tell us whether gain of is greater than gain of , and vice versa .we get the formula out of our general assumptions without any arbitrariness .actually , the utility function $ ] is uniquely determined by the geometry ( or a system of open balls ) of the space , since for the norm we can construct the functional with the required properties .further , the relation continues to hold if we replace the constant by .then to each relative gain we can assign a well - known kolmogorov smirnov statistic , thus : setting we obviously get new metric of .trivially , that norms and are equivalent in .this introduces the next crucial point in our model .let be a sample of physics journals .the formal definition of the _ remoteness _ from a journal to is the following : where denote the difference between and .we can see more clearly the geometrical significance of the above definition .the formula means that is the distance from to the ( non - empty ) set corresponding to the sample .incidentally , we may notice that .the _ diameter _ of a journal can be defined as the least upper bound of : for the sj model , two quantities are needed : the remoteness and the diameter .we can use the concept of ordered pair to define a situs of a journal .  at the same time , the notion of the spj is more abstract than it need be .this leads us to introduce a new term : `` map of the spj '' .it denotes a set , each member of which is an ordered pair . more precisely , the map of the spj is a pair consisting of a metric subspace and a set of all ordered pairs .the sj characterises the structure of citations of a journal relative to a sample of journals .thus , it is certainly legitimate to represent the spj as the map of the spj .in general , there is no unique way of presenting in a more practical form .however , to a first approximation , we can obtain an estimate of by using of the ratio between and : having jif higher than marked by numbers . list of journals see in appendix 1 . ]we first begin our empirical exploration with a small but significant formal result : fig .[ fig:1 ] shows that is highly correlated with ( pearson s ) .also it is seen that the relationship is linear and positive .furthermore , is highly correlated with the median of ( pearson s ) ( cf . ) .   in this article, the visualisation of the spj is based on the use of multidimensional scaling ( cf . ) . to analyse andvisualise the pattern of similarity between the physics journals , the multidimensional scaling method was applied to the distance matrix .multidimensional scaling enables us to reduce the dimensionality of the initial space of journals .we constructed a two - dimensional common space of physics journals , which satisfactorily describes the initial matrix of distances between journals .this reduces a system of interconnected differences between journals to two generalised `` axes '' , shown in fig .[ fig:2 ] .the coordinate axes of the common space of physics journals are scientometric invariants of the sample .these axes express the foundations of the classification of physics journals , which is generated by the system of scientometric differences .the axis of the common space of physics journals correlates with the quantity ( pearson s ) , while the axis correlates with the quantity ( pearson s ) .physics journals .plot of the first and second coordinates of multidimensional scaling analysis ( with the use of the proxscal algorithm ) of distances ( ) .journals having jif higher than marked by numbers .list of journals see in appendix 1 . ]the spj is a relational multi - level system .each level of relations in the spj encloses a certain selection of scientometric data into a logical whole .the aim of our analysis of the common space of physics journals is not to portray the multitude of physics journals as the manifestation of a single principle of structuring scientific communication in physics .rather , we aim to establish a constructive relationship between the journals , which manifests itself as an opportunity to move from any position in the common space of physics journals to all the others .journals located in the different quadrants vary by size , citation level , impact factor , and the length of time they have been indexed in the wos cc . as a result , they enjoy different levels of popularity and prestige .in fact , when moving clockwise from quadrant i to quadrant ii the properties of the journals changes monotonically .the average value of jif for journals of quadrant i is equal to , for journals of quadrant iv  ; for journals of quadrant iii and quadrant ii the average value of jif is and respectively .the total number of citations received by a journal in the wos cc changes analogously .the average value for the indicator total cites for journals of quadrant i is equal to ; for publications of quadrant iv  .the lowest average value of total cites is observed among the journals of quadrant iii and quadrant ii , where the value of the indicator is and respectively .the highest average value of variance can be observed in quadrant i and quadrant ii , where it is and respectively .the differentiation of articles by level of citation in these two quadrants is very high . in this respectthey differ from the journals in quadrant iv and quadrant iii , which are more homogenous . for the latter ,the average variance in the level of citation is and .the indicator for the number of citable items in two years behaves somewhat differently . on average , the journals of quadrant i publish papers , and the journals of quadrantiv  .the figures for journals of quadrant iii and quadrant ii are significantly less ; on average , they publish and citable items in two years .we can note an important feature of the journals in quadrant i. by comparison with the others these are relatively new journals .the average year of their foundation is 1995 .these journals are mainly products of the era of the internet and bibliometric databases .they are more in line with modern tools for the dissemination of scientific information better than other journals .this may be one of the factors that contributes to their high bibliometric indicators .the journals in quadrant i are `` journals of quality '' , if one goes by their citation statistics .the structure of the common space of physics journals contains information on certain qualitative characteristics of journals .for example , of journals in quadrant ii have open access status .in all the remaining quadrants their share does not exceed .this state of affairs is consistent with the results of scientometric studies , which have demonstrated that the openness of scientific publications does not automatically lead to a higher level of citation ( cf . ) . in the case of physics journals ,the majority of open access publications have a relatively low level of citation . even in quadrant ii ,open access journals do not enjoy a higher level of citation than those which maintain a traditional copyright policy .the average citation level for those journals in quadrant ii which have open access status is total cites , while the remaining journals in this group have on average total cites .it can be suggested that journals consider open access status to be a means of increasing their popularity , but the citation rates of these journals suggest that open access in itself is no guarantee of increased citation .the common space of physics journals acts as a kind of meta - language for the description of journals , which enables us to identify regularities through analysis of their properties in a fixed `` alphabet '' of quadrants .thus , when it comes to publishers of journals , certain regularities can be observed when moving in a clockwise direction through the common space of physics journals .  although publishers sophisticated strategies are constantly changing the landscape , we attempt to map these regularities .quadrant i is dominated by journals which belong to academic institutions : american chemical society , institute of physics , royal society of chemistry , and tsinhua university .the publisher springer nature is the exception to this .as we move from quadrant i to quadrant ii , the influence of scientific publishing companies increases . in the quadrantiv , scientific publishing companies begin to predominate .elsevier , springer nature and wiley blackwell have a share of of all journals in the quadrant .however , leading physics societies also enjoy a significant position .journals published by institute of physics account for , while american physical society and american institute of physics have shares of and respectively .quadrants iv and iii can be considered the `` world of elsevier '' .the large majority of this publisher s journals ( ) can be found in these quadrants . in quadrantiii , the share of journals owned by large multinational publishers increases , while the share of journals belonging to professional societies decreases .the share of journals published by institute of physics , american physical society and american institute of physics is just in quadrant iii , while the proportion of journals belonging to elsevier , springer nature and wiley blackwell is .quadrant ii differs substantially from the three preceding quadrants .the first striking characteristic is the concentrated presence of the scientific publishing company maik nauka , which publishes translations of russian journals .all of this publisher s journals can be found in quadrant ii , accounting for of all journals in this quadrant .all journals published by world scientific can also be found in this quadrant  of the total .the third major publisher in quadrant ii is springer nature , with a share of .elsevier is weakly represented in this quadrant , with a concentration of just .   in coordinates of and .journals having jif higher than marked by numbers .list of journals see in appendix 1 . ]due to the strong internationalisation of the publishing process , it is not possible to straightforwardly classify physics journals in terms of national affiliation .however , it is possible to trace the distinction between `` global '' and `` local '' , which is formed on the principle of `` the west and the rest '' . in moving from quadrant i to quadrant ii the number of countries to which a journal can be ascribed rises . in quadranti the only countries represented are the usa , great britain , germany and china .quadrant iv contains eight countries , of which the netherlands ( to which elsevier is affiliated ) occupies a prominent place .the most international quadrant in terms of publisher affiliation is ii , which contains journals affiliated with countries . besides the usa and great britain , russia and singapore play a significant role in this quadrant( home respectively to the publishers maik nauka and world scientific ) .  also , the common space of physics journals is not only a geometrical locus of relations between citations , but also between those social forces which aim at transforming these relations .the common space of physics journals can be treated , amongst other things , as a projection of competitive relations within the triad `` transnational publishers  professional physics societies  regional publishers '' ( cf. ) :  * in quadrant i professional physics societies are dominant . * in quadrant iv there is interference of professional societies and transnational publishers .* quadrant iii is dominated by transnational publishers , while professional physics societies have a relatively weak representation .* in quadrant ii the dominant players are regional publishers from asia , latin american and the former soviet union , while the role of professional physics societies and transnational publishers is insignificant .the journals of the second quadrant are those which stem from `` non - western '' science , which are less well adapted than others to the demands of global physics and the wos cc .journals according to values of are shown in fig .[ fig:3 ] .we include the results of the analysis of the common space of physics journals in the next stage of our research as an empirical knowledge . in this way, we give the relational definition to empirical data and organise them . from fig .[ fig:3 ] it can be clearly seen that the structure of the common space of physics journals accords with the distribution of . for the sake of continuity , in fig .[ fig:3 ] the journals are marked using colours , which correspond to the four quadrants in fig .[ fig:2 ] .the journals of quadrant i still significantly differ from the others , having higher values on the axis ._ nature photonics _ ( 149 ) and _ nature physics _( 150 ) particularly stand out in this respect .the remaining publications form a monotonic sequence in which the journals from quadrant ii gradually take the place of the journals from quadrant iii , and finally the journals from quadrant iv .let us describe this sequence , digressing briefly from `` journals of quality '' .   in coordinates of and .journals having the variance of citations higher than marked by numbers .list of journals see in appendix 1 . ]  around of the total sample of physics journals are located within a diagonal band running from the top - left to the bottom - right . in the upper part of this `` main sequence ''we find journals with a low jif ( e.g. , _ journal of infrared and millimeter waves _ ( 98 ) , _ bulletin of the lebedev physics institute _ ( 23 ) , _ journal of applied mechanics and technical physics _( 92 ) , _ moscow university physics bulletin _ ( 143 ) ) , while the bottom - right contains those with a high jif ( e.g. , _ journal of high energy physics _( 97 ) , _ physics letters b _ ( 190 ) , _ physical review e _ ( 184 ) , _european physical journal b _ ( 55 ) ) . moving along the `` main diagonal '' from top to bottom, we move in turn from journals located in quadrant ii in fig .[ fig:2 ] , to those located in quadrant iii , and finally to those of quadrant iv .this means that we are moving to journals with a successively higher jif .separately , above and to the right of the `` main diagonal '' lies a group of journals with `` abnormally '' high jifs .all ten journals which form this group belong to quadrant i.   scientific publishers .plot of the first and second coordinates of multidimensional scaling analysis ( with the use of the alscal algorithm ) of distances ( ) . ]  from fig .[ fig:3 ] it can be seen that the minimum values of and the maximum values of correspond to journals with a high jif .the smaller the value of and the larger the value of , the higher its `` force of attraction '' , and the more journals from try to resemble it .it is no coincidence that the journals of quadrant iv  i.e. well - established , reputable physics journals  can be found in the rectangle , which corresponds to large values of and small values of . at the same time, journals with a low jif can be found in the rectangle representing high values of and low values of .[ fig:4 ] provides a visualisation of the connections between and journals national affiliation .journals affiliated to the usa , great britain , the netherlands and germany are located in the area , which corresponds to high values of and low values of .these are `` points of attraction '' of the sample , having a large remoteness and a small diameter .in contrast , publications affiliated with china , singapore , russia , egypt and poland are located in the area , which combines low values of with large values of .it can be noted in particular that certain journals try to gain affiliation with the usa or great britain in a bid to increase their status .this fact makes the distinction between global and local ( which we pointed to in our analysis of the map of the spj ) less significant , if the national affiliation of a publisher is determined only by formal factors .the area , which corresponds to small values of and large values of , contains journals which _ de jure _ are affiliated to the usa , but _ de facto _ are connected with russia : see , e.g. , _ bulletin of the lebedev physics institute _ ( 23 ) , _ moscow university physics bulletin _ ( 143 ) , _ russian physics journal _ ( 220 ) , and _ mechanics of solids _the same can be said about _chinese physics c _ ( 33 ) and _ chinese physics letters _ ( 34 ) , published by the chinese physical society , but affiliated to the uk .consecutive movement to the right along the axis and downwards along the axis coincides with an increase in the time span over which a journal has been indexed in the wos cc .journals which have a significantly longer time span of indexation in the wos cc lie in the rectangle which combines large values of with small values of . by contrast , those journals which are located in the rectangle with low values of and high values of have a shorter time span of indexation in the wos cc .  fig .[ fig:3 ] and fig . [ fig:4 ]allow us to state that the distribution accords with the distribution of journals characteristics . in moving along the main sequence, a shift takes place from high impact factor journals to low impact factor journals ; from global to regional ; from journals with a longer time span of indexation in the wos cc to those with a shorter time span of indexation in wos cc .`` newcomer giants '' , to whom these dependencies do not extend , are situated apart from the main sequence .while long - term strategies of merger and acquisition can disrupt patterns of similarity between publishers , the citation rates of journals belonging to one publisher often show statistical similarities .we analysed main publishers from the sample , which accounted for of all journals . in order to represent relationships between the scientific publishers ,the multidimensional scaling method was applied .[ fig:5 ] is the plot of the first and second coordinates of multidimensional scaling of the matrix of hausdorff distances between all pairs of the publishers .the axis in fig . [ fig:5 ] polarises publishers according to . on the right poleare springer nature ( transnational ) , american chemical society ( us ) , american physical society ( us ) , wiley blackwell ( transnational ) .it is these publishers journals which lie in quadrant i in fig .[ fig:2 ] . on the left poleare publishers which do not have journals with high values of : the american institute of physics ( us ) , hindawi ( egypt ) , science press ( china ) , edp press ( france ) , maik nauka ( russia ) . only two american scientific societies which are global players in the scientific field fall into the area with negative values of ; the remainder are regional players .   against average .]  the axis in fig .[ fig:5 ] provides a visualisation of the differences between scientific societies and commercial publishers . at the top of the axisare the american chemical society ( us ) , the american physical society ( us ) , the institute of electrical and electronics engineers ( us ) , the optical society of america ( us ) . at the bottom of the axisare the largest of the transnational publishers : springer nature ( transnational ) , elsevier ( transnational ) and taylor & francis ( transnational ) , as well as world scientific ( singapore ) .of the scientific societies , only the united kingdom s institute of physics is located in this area .it can be suggested from fig .[ fig:5 ] that the space of physics publishers is structured around two fundamental oppositions :  1 .the first opposition centres around traditional and american publishers on the one hand , which publish `` high ranking '' journals in the sphere of `` mainstream '' global research agendas , contrasted with mainly regional publishers on the other hand , which own journals aimed at more `` niche '' readerships and cover the results of less topical research .2 .  the dominant role in the second key oppositionis played by the differences separating the professional societies of mainly american origin , and the transnational commercial publishers originating from europe .let us consider the publishers themselves in the map of the spj . as can be seen from fig .[ fig:6 ] , publishers are situated relative to each other in an orderly manner . moving from the lowest average values of to the highest , and simultaneously from the highest average values of to the lowest , it can be observed that regional publishers give way to traditional ones , which in turn are displaced by publishers belonging to professional societies .thus , a `` competitors triangle '' ( cf . ) is reproduced in the system of coordinates   between regional publishers  transnational publishers  professional societies .the suggested approach to scientific quality of a physics journal is more like a mode of reasoning , characterised by free exchanges between empirical and analytical arguments , rather than a `` hypothetico - deductive '' model .the spj should not be taken as the definition of scientific quality of a journal in the sense of basic sciences . in the worst casethis scientometric notion represents social stereotypes , everyday knowledge or business demands ; in the best case it implies them but is not implied by them .the spj is not a guideline for scientometric research programmes , but an attitude towards the field of physics itself .of course , the use of the spj is significant not because the distance matrix constitutes a `` scientific quality '' , but because we believe that by using the spj we will learn something about the regularities that govern scientific field .  from our relational point of view, the quality of a physics journal exists only in reference to other journals . since the issue we are seeking to addressis concerned not with individual journals , but rather with the totality of journals and the interrelations between them , it should come as no surprise that the resultant working model is the spj . in the given context ,the spj is a mathematical construct that relates different elements within the entire data set to each other , and thereby produces a single scientometric entity .the spj as metric space _sui generis _ is a natural generalisation of the concept of closeness of physics journals .it is a heuristic approach based on an abstract assumption ( covering a wide range of concrete phenomena ) for which there is no fundamental theoretical justification .  in summary, the totality of physics journals can be represented in the form of the spj . in studying physics journals as the spj, we are abstracting from that to which physics journals owe their existence , in the form of subjects of scientometric research .each journal is characterised through negation . broadly speaking, a physics journal is defined by that which distinguishes it from all other journals . by virtue of this ,the system of distances which differentiates edfs also expresses the system of conditions for the existence of physics journals .this system is inscribed in the totality of social relations which constitutes scientific field .the spj we have constructed describes scientometric data on journals in a compact form .moreover , the spj models certain regularities to which journals conform .thus , the spj provides an objective basis for the grouping of physics journals on the basis of a whole range of indicators .this makes it possible to analyse the structure of the spj . in turn , this structure sheds light not only on journals as direct forms of scientific communication , but also reveal the structuring role of publishers , something which is not usually highlighted .analysis of the spj allows us to advance the hypothesis that the structure of its positions is determined by a system of relations between publishers .publishers are only able to structure the spj because they themselves are structured :  * agents of the spj differ , firstly , by whether their research activity is carried out by self - organised groups of scholars , or as a member of an organisation which seeks to make a profit .it is a matter of distinguishing between collectively - produced collective products , and products produced by a relatively autonomous field of publication production and circulation .* secondly , agents differ in terms of volume of economic capital , which in our case manifests itself most clearly in the opposition between global and local players in the spj .  we hope that this paper offers a new and easy way of studying scientific journals to anybody who treats it mathematically .the prompted method differs from those usually employed .the article was prepared within the framework of the basic research program at the national research university higher school of economics ( hse ) and supported within the framework of a subsidy by the russian academic excellence project `` 5 - 100 '' .48 natexlab#1#1[1]`#1 ` [ 2]#2 [ 1]#1 [ 1]http://dx.doi.org/#1 [ ] [ 1]pmid:#1 [ ] [ 2]#2 , & ( ) . . , _ _ , . ., , et al .( ) . . , _( ) . . , __ , . . , & ( )( ) . . , __ , . . , & ( )springer series in statistics ( ed . ) . : .http://dx.doi.org/10.1007/0-387-28981-x . ., , , , & ( ) . . , __ , . . , & ( )http://ieeexplore.ieee.org/xpl/bkabstractplus.jsp?bkn=6825200 . ,& ( ) . . , _ _ , . .( ) . . in , & ( eds . ) , _ _ ( pp . ) . : ., , , , & ( ) . . , _, , & ( ) . . ,( ) . . : http://www.garfield.library.upenn.edu/ci/title.pdf .( ) . . , __ , . . , & ( )_ , . . , & ( )_ , . . , & ( )( ) . . , _, , , , & ( ) . . , __ , . . , & ( ) .volume of _ _ . : . .( ) . . , __ , . . , , & ( ), , , , , , , , & ( ) . . , . .( ) . . , _, , , & ( ) . . , _ _. http://arxiv.org/abs/1603.08452 . ,& ( ) . . in ( ed . ) , _ _ ( pp . ) . : .( ed . ) . http://dx.doi.org/10.1016/b978-0-08-097086-8.85030-8 . ., , & ( ) . , _, , , , & ( ) . . , __ , . . , & ( )_ , . . , & ( )( ) . volume  of _ _ . : . ., ( p. ) . ., , , , & ( ) . . , _volume of _ _ .( ed . ) . : . ., , , & ( ) . . : . . ,& ( ) . . in , & ( eds . ) , _ _ computational social sciences ( pp . ) . : . .( ) . . , _, , & ( ) . . , _, , & ( ) . . , _, , , , , & ( ) . . , _ _ . .thomson reuters ( ) . .http://wokinfo.com/essays/impact-factor/ . ,& ( ) . . : . .( ) . . , _( ) . . , __ , . . , , , & ( ) ., , & ( ) .in _ _ racs ( pp . ) . : . .1 .  acoustical physics 2 .acs photonics 3 .acta acustica united with acustica 4 .acta physica polonica a 5 .acta physica polonica b 6 .acta physica sinica 7 .advances in condensed matter physics 8 .advances in high energy physics 9 .advances in mathematical physics 10 .american journal of physics 11 .annalen der physik 12 .annales henri poincare 13 .annals of physics 14 . applied acoustics 15 . applied optics 16 . applied physics a - materials science & processing 17 .applied physics b - lasers and optics 18 .applied physics express 19 . applied physics letters 20 . applied radiation and isotopes 21 .archives of acoustics 22 .brazilian journal of physics 23 .bulletin of the lebedev physics institute 24 .canadian journal of physics 25 .central european journal of physics 26 .chalcogenide letters 27 .chaos solitons & fractals 29 .chinese journal of chemical physics 30 .chinese journal of physics 31 .chinese optics letters 32 .chinese physics b 33 .chinese physics c 34 .chinese physics letters 35 .classical and quantum gravity 36 .communications in computational physics 37 .communications in mathematical physics 38 .communications in nonlinear science and numerical simulation 39 .communications in theoretical physics 40 .comptes rendus physique 41 .computer physics communications 42 .condensed matter physics 43 . contributions to plasma physics 44 .cryogenics 45 .current applied physics 46 .doklady physics 47 .ecs journal of solid state science and technology 48 .ecs solid state letters 49 .entropy 50 .european journal of physics 52 .european physical journal applied physics 53 .european physical journal special topics 54 .european physical journal a 55 .european physical journal b 56 .european physical journal c 57 .european physical journal d 58 .european physical journal e 59 .european physical journal plus 60 .ferroelectrics 61 .few - body systems 62 .fortschritte der physik - progress of physics 63 .foundations of physics 64 .frontiers of physics 65 .general relativity and gravitation 66 .high energy density physics 67 .high pressure research 68 .high temperature 69 .ieee journal of quantum electronics 70 .ieee photonics journal 71 .ieee photonics technology letters 72 .ieee transactions on applied superconductivity 73 .ieee transactions on magnetics 74 .ieee transactions on nuclear science 75 .ieee transactions on plasma science 76 . imaging science journal 77 .indian journal of physics 78 .indian journal of pure & applied physics 79 . infrared physics & technology 80 .international journal of geometric methods in modern physics 81 .international journal of modern physics a 82 .international journal of modern physics b 83 .international journal of modern physics c 84 .international journal of modern physics e - nuclear physics 85 .international journal of photoenergy 86 .international journal of quantum information 87 .international journal of theoretical physics 88 .inverse problems 89 .ionics 90 .japanese journal of applied physics 91 .jetp letters 92 .journal of applied mechanics and technical physics 93 .journal of applied physics 94 .journal of chemical physics 95 .journal of computational physics 96 .journal of experimental and theoretical physics 97 .journal of high energy physics 98 .journal of infrared and millimeter waves 99 .journal of low temperature physics 100 .journal of luminescence 101 .journal of magnetics 102 .journal of magnetism and magnetic materials 103 .journal of mathematical physics 104 .journal of modern optics 105 .journal of nanophotonics 106 .journal of non - crystalline solids 107 .journal of optics 108 .journal of phase equilibria and diffusion 109 .journal of physical chemistry c 110 .journal of physics - condensed matter 111 .journal of physics a - mathematical and theoretical 112 .journal of physics and chemistry of solids 113 .journal of physics b - atomic molecular and optical physics 114 . journal of physics d - applied physics 115 .journal of physics g - nuclear and particle physics 116 .journal of plasma physics 117 .journal of rheology 118 .journal of statistical mechanics - theory and experiment 119 .journal of statistical physics 120 .journal of superconductivity and novel magnetism 121 .journal of synchrotron radiation 122 .journal of the acoustical society of america 123 .journal of the european optical society - rapid publications 124 .journal of the korean physical society 125 .journal of the optical society of america a - optics image science and vision 126 .journal of the optical society of america b - optical physics 127 .journal of the optical society of korea 128 .journal of the physical society of japan 129 .journal of x - ray science and technology 130 .laser & photonics reviews 131 .laser and particle beams 132 .laser physics 133 .laser physics letters 134 .letters in mathematical physics 135 .low temperature physics 136 .magnetohydrodynamics 137 .mechanics of solids 138 .metrology and measurement systems 139 .micro & nano letters 140 .modern physics letters a 141 .modern physics letters b 142 .molecular physics 143 .moscow university physics bulletin 144 .nano letters 146 .nano research 147 .nanoscale 148 .nanoscale research letters 149 .nature photonics 150 .nature physics 151 .new journal of physics 152 .nuclear data sheets 153 .nuclear fusion 154 .nuclear instruments & methods in physics research section a - accelerators spectrometers detectors and associated equipment 155 .nuclear instruments & methods in physics research section b - beam interactions with materials and atoms 156 .nuclear physics a 157 . nuclear physics b 158 . nuclear science and techniques 159 .nukleonika 160 .optical review 161 .optics communications 162 .optics express 163 .optics letters 164 .optik 165 .organic electronics 166 .phase transitions 167 . philosophical magazine letters 168 .philosophical transactions of the royal society a - mathematical physical and engineering sciences 169 .photonics and nanostructures - fundamentals and applications 170 .physica a - statistical mechanics and its applications 171 .physica b - condensed matter 172 .physica c - superconductivity and its applications 173 .physica d - nonlinear phenomena 174 .physica e - low - dimensional systems & nanostructures 175 .physica scripta 176 .physica status solidi - rapid research letters 177 .physica status solidi a - applications and materials science 178 .physica status solidi b - basic solid state physics 179 .physical review a 180 .physical review applied 181 . physical review b 182 . physical review c 183 . physical reviewphysical review e 185 .physical review letters 186 .physical review special topics - accelerators and beams 187 . physical review x 188 . physics - uspekhi 189 .physics letters a 190 .physics letters b 191 .physics of atomic nuclei 192 .physics of fluids 193 .physics of particles and nuclei 194 .physics of plasmas 195 .physics of the solid state 196 .plasma physics and controlled fusion 197 .plasma physics reports 198 . plasma science & technology 199 .plasma sources science & technology 200 .powder diffraction 201 .pramana - journal of physics 202 .proceedings of the royal society a - mathematical physical and engineering sciences 203 .progress in natural science - materials international 204 .progress of theoretical and experimental physics 205 .quantum electronics 206 .quantum information & computation 207 .quantum information processing 208 .radiation effects and defects in solids 209 .radiation measurements 210 . radiation physics and chemistry 211 . radiophysics and quantum electronics 212 .rendiconti lincei - scienze fisiche e naturali 213 .reports on mathematical physics 214 .reports on progress in physics 215 .revista mexicana de fisica 216 .rheologica acta 217 .romanian journal of physics 218 .romanian reports in physics 219 .russian journal of physical chemistry b 220 .russian physics journal 221 .science china - physics mechanics & astronomy 222 . semiconductor science and technology 223 . semiconductors 224 .solid - state electronics 225 .solid state communications 226 .solid state ionics 227 .solid state sciences 228 .studies in history and philosophy of modern physics 229 .superconductor science & technology 230 . superlattices and microstructures 231 .surface and interface analysis 232 . surface review and letters 233 .surface science 234 .symmetry integrability and geometry - methods and applications 235 .synthetic metals 236 . technical physics 237 . technical physics letters 238 .theoretical and mathematical physics 239 .thermophysics and aeromechanics 240 . wave motion

Abstract: this paper analyses the problem of scientific quality of physics journals . the main assumption is that the quality of a physics journal exists only in reference to other journals . instead of constructing new indicators of scientific quality , we identify a physical journal with corresponding empirical distribution function of citations . from our relational point of view , the space of physics journals is only a system of differences between empirical distribution functions of citations . using data from web of science core collection we consider the space of physics journals and the space of scientific publishers . the first provides an objective basis for the grouping of physics journals on the basis of a whole range of indicators ( citation statistics , country , publisher , etc . ) . the second reveals the `` competitors triangle '' of regional publishers , transnational publishers and professional physical societies . these findings have prompted us to advance the hypothesis that the structure of the space of physics journals is determined by a system of relations between publishers .   citation analysis , scientometric indicators , scientific quality of a journal , space of journals , scientific publishers , 91d30 , 91d99


the concept of particle flow algorithms ( pfa ) and the beam structure of the planned international linear collider ( ilc ) accelerator put constraints on the data acquisition ( daq ) system which are described in the following .pfa is a widely accepted approach to improve the energy resolution at the ilc .particle flow uses the high segmentation of about 1 cm ( or smaller ) in the detection layer of a sampling calorimeter to track particles through the calorimeter .the segmentation results in about 24 million readout pads in the electromagnetic calorimeter ( ecal ) of a planned ilc detector . because of the large number of readout channels it is necessary to minimise the cost of the electronics .this is achieved by using standard networking chipsets and protocols .already at an early stage of the calorimeter prototypes the daq system has been designed for scalability . in the current detectorplans the space for the electronics and cooling inside the calorimeters is very restricted .the daq system under development is aiming at a generic daq system , which will be applicable for the ecal , analogue hadronic calorimeter ( ahcal ) and digital hadron calorimeter ( dhcal ) prototypes . at the ilcit is assumed that all data will be collected with no triggers implemented . during a bunch train, data will be stored on the detector and then read out during the inter - train gap of about 200ms .the data are taken by the detectors on the detection slabs and digitised by the very front - end on - detector electronics or slabs .then all output data are delivered to electronics boards at the end of the detector .data is then sent to a concentrator card which collects data from many detector units before being sent off the detector on gigabit optical fibres to a detector receiver in the counting room .figure[fig_daqoverview ] gives an overview of the generic daq scheme .the calorimeter is designed such that vfe chips are embedded in the detector slabs .the slabs are served from the ends with a detector interface ( dif ) .the difs transmit the data to the link - data aggregator ( lda ) which is fitted on - detector and serves many difs via standard hdmi links .the data from the ldas are fed to the off - detector receiver ( odr ) via the gigabit optical cables .the odr is a dedicated pci - express card which is hosted in a daq pc , being capable of saving the data to central storage .the detector signals are buffered and digitised by the vfe asics situated on the detector slabs .the vfe asics depend on the detector used in the prototypes accommodating the different features of each detectors .the interface between the vfe and the daq system is provided by the dif board which is located at the end of the calorimeter slabs .the dif board consists of a customised part which translates the signals of the asics into more generic signals which are independent of the detector used for the calorimeter .the interface has been defined together with three detector groups working on prototypes for the ecal , ahcal and dhcal within the eudet project and is common to the three different detector types . a generic part of the dif passes the data on and sends configuration on to the vfe electronics .hdmi is a home entertainment system standard with small cabling and connectors which are commercially available at low cost .they are rated at more than 300mb / sec for data . to provide redundancy against link failures ,a provision is made on the dif to connect to its neighbour . by connecting even and odd difs to different ldas, the system is protected for the loss of a dif - lda link , or even the failure of an entire lda .   in order to accumulate the data sent from the dif ,an lda collects the data from several difs and sends it further to the odr .the number of difs aggregated in the lda depends on the detector type chosen in the detection layer. the optimal number of difs / lda should take into account the number of available pins on the fpga , the bandwidth per dif and the effective performance - price ratio to maximise bandwidth of the optical link .the current lda prototype can host up to eight links to the difs with a small upgrade up to ten dif connections .the lda has banks of hdmi connectors for connections to the difs and a small form - factor pluggable ( sfp ) connector for the optical link off - detector .the prototype version of the lda is built on a commercial development board with a xilinx spartan3 - 200 fpga .the two sets of connectors are physically add - on boards : one providing the sfp and serialiser chipset for the optical link , the other hosting eight working hdmi connectors with clock fan - out hardware .a first prototype of the lda has been produced by the company enterpoint and has been thoroughly tested .the lda is situated at the edge of the detector , the odr however is located in the counting room connected to the on - detector daq system by an optical fibre . as well as receiving data from the detector , it sends control and configuration data to the lda for distribution to the difs and finally sends the data off the detector to the event building .it is realised as a pci - express card and can serve up to four ldas per card , with one pc hosting up to two odrs .for the proposed daq system currently a xilinxvirtex4 fpga is used , thereby using a commercial fpga board designed by plda . at present , the data stream which will come from the detector in the eudet test beam is simulated by an internal data generator in the firmware or via an on - board ethernet interface ; this allows for a thorough debugging and optimisation of the system before integration with the detectors .the user interface to the odr card contains two parts : a customised driver and a client program .the former is mainly tasked with mapping card memory to the user space and providing direct memory access ( dma ) support .the latter client retrieves data from the odr card memory and stores it on the local disk .the performance of the prototype odr has been investigated using an ethernet interface to provide an input data stream which is copied to host memory and is currently higher than 150 mb / s writing to an array of disks. a higher data rate of up to 700mb / s can be achieved when writing into the host memory .the number of dmas has been optimised for the performance .the odr prototype is ready and can be optimised further in the next months .for the event building a good clock is essential because the events will be built using time stamps .it is understood that a machine clock will be fed into the odrs and fanned out to the ldas and difs .the requirements on the clock are a low jitter and a fixed latency between the machine clock and the clock in the difs .commercial networking hardware is not suited for this task as it is most efficient when it can buffer data and provides no guarantees on delivery times . similarly networking hardware built into modern fpgas suffers from varying latency .therefore a clock and control ( c&c ) board has been designed with links to eight odrs .the c&c logic is implemented on a board with 6u format , translating into a board size of 100mm mm .the clock and control module must interface with the machine and provide stand - alone signal and clock generation .the machine clock is expected to run between 50 and 100mhz .the bunch clock will be derived as a multiple of the machine clock .it is able to deliver fast asynchronous triggers .it will also receive a busy signal from the vfe .the hdmi cables used for the dif to lda link will be reused here for sending control data .the c&c board has been delivered and has been successfully tested . in parallel the firmware for the c&c board is being developed .the most important requirement on the daq software for the calorimeters is its scalability . in order to minimise risks and to shorten development timea well - established software framework will be used .doocs was found to be suitable for our daq needs .  to adapt doocs to the requirements of our daq softwarethe equipment name server ( ens ) has been used to integrate all daq components into one system .ens provides services for naming resolution and rpc communication . in the naming structure of ensall the functionalities and properties for each device have to be classified and defined . as seen in fig.[fig_daqoverview ] , the odr is the first hardware layer which can communicate with doocs .therefore the software for the odr has been the starting point of the daq software development .the doocs client provides a list of commands and configurable parameter with which the odr devices can be managed .configuration data and files are used when the system starts and runs .a prototype for the odr doocs client has already been shown . to steer the whole system with the doocs control software several further developments are in progress .the daq system for the eudet detector will be a hierarchical daq system which minimises the space needed on the detector and uses commercial components to minimise the cost of the daq system . in order to make the development forthe test system independent of the detector type tested a dif board will make the readout generic .an lda card will concentrate the data from the dif and send it off to the odr which is located off the detector in a control room .the task of the odr is to store the data .all components have in addition the task to send configuration data and control messages to the detector and all other daq components upstream .at the time of writing each hardware component of the daq system exists and has been tested ; the individual components now need to be integrated into a complete system .current tests have shown that the daq software is able to integrate the odr into the daq system based on the existing software framework doocs and manage successful communication and control tests .the goal is to have the whole daq system ready for a test beam in 2009 .we would like to acknowledge the support of the commission of the european communities under the 6th framework programme `` structuring the european research area '' , contract number rii3 - 026126 .99 tesla technical design report , part iv , a detector for tesla , t. behnke et al . , 2001 eudet - detector r&d towards the international linear collider , eudet homepage : + http://www.eudet.org/ hdmi- high definition multimedia interface consortium homepage : + http://www.hdmi.org enterpoint , fpga and asic design , homepage : + http://www.enterpoint.co.uk plda homepage : + http://www.plda.com/index.php doocs , distributed object oriented control system homepage : + http://tesla.desy.de/doocs/doocs.html linear collider .

Abstract: a data acquisition ( daq ) system is described which will be used for the next generation of prototype calorimeters using particle flow algorithms for the international linear collider ( ilc ) . the design is sufficiently generic and scalable such that it should have numerous applications either for ilc detectors or elsewhere within high energy physics in general . the daq system will be implemented using fpgas and built using off - the - shelf components and networking hardware with programmable fpgas . the software for the daq system is based on an existing framework , doocs , which is a server / client object - oriented system . the design philosophy , current status of the project and its aims are presented in this report .