with time - completely at odds with the second law! this generally - held misconception that change of entropy is fundamentally time - asymmetrical is revealed by the loschmidt paradox. the loschmidt paradox considers the apparently fundamental time - asymmetry of entropy implied by the second law and states that this is at odds with the known time symmetry of fundamental processes. it is only when we realise that the second law is frequently badly stated and hence contains unstated assumptions ( which have been just considered ) that the loschmidt paradox is resolved. ( wikipedia describes this resolution of the paradox, showing how one of the key assumptions of boltzmann ' s version of the second law of thermodynamics was flawed - see here ). but if change of entropy is time - symmetric, why do we see the entropy of the universe as only increasing? roger penrose considers this question in his book the road to reality. penrose considers what we might expect to happen if we trace the entropy of the universe back in time from the state it is in now. if change of entropy is really time - symmetrical, then we should expect to see entropy increasing as we trace the universe into the past, just as we will see entropy increasing into the future. but we know, in fact, that the universe had a lower entropy in the past : i. e., the entropy of the universe actually reduces in the past. so where does this asymmetry come from? as roger penrose goes on to reveal, the time - asymmetry of change of entropy within the universe is explained by the extraordinarily low entropy of the universe at its origin : basically, the low - entropy past of the universe " fixes " the experiment. if we want to get a symmetrical answer then we have to be careful to conduct a symmetrical experiment. rather than starting with a special - case low entropy universe, we have to imagine a universe which started in thermal equilibrium and has reached its current state unaided, purely by chance : after that low - entropy point is reached, we then see entropy starting to increase according to the second law. but the key thing is that if we trace the entropy of the universe back in time past the low - entropy point we now see that symmetry that roger penrose sought. hence, change of entropy is fundamentally symmetrical. in fact, throughout this discussion on the arrow of time we will find that the arrow of time is caused by the time - symmetric second law of thermod


see that symmetry that roger penrose sought. hence, change of entropy is fundamentally symmetrical. in fact, throughout this discussion on the arrow of time we will find that the arrow of time is caused by the time - symmetric second law of thermodynamics, together with the very special, low - entropy initial conditions of the universe. ( this discussion on time - symmetric entropy change is based on an example by j. richard gott in his book time travel in einstein ' s universe in which the role of the universe is played by an ice cube - see here. the ice cube example is considered in detail in chapter 6 of brian greene ' s book the fabric of the cosmos. ) we all have a very strong feeling of a directionality of time, which has a flow in a forwards direction. as michael lockwood says in his book the labyrinth of time : " we regard the forward direction in time, in stark contrast to the backward direction, as the direction in which causality is permitted to operate. causes, we assume, can precede their effects, but cannot follow them. " but we have just seen how physical processes appear to be time - symmetrical, with no distinction between the forward and backward directions. so where does that leave causality? as michael lockwood again says about the passage of time : " we find no hint of this in the formalism of newtonian physics. not only is there no explicit reference to a passage or flow of time ; there is not even any reference to cause and effect. indeed, there is not even any directionality ". " but ", you might protest, " surely causality works in only one direction : forwards in time? i kick a football - the football doesn ' t kick me. " well, let ' s consider the example immediately below of forward causality. we see a snooker cue coming in from the left, hitting the white ball, which then causes the white ball to hit the red ball : however, if you shoot a movie of that sequence, and then play it backwards, it still makes perfect physical sense. as you can see below, we then have the red ball coming in from the right, hitting the white ball, which then causes the white ball to hit the cue backwards. so, because of the symmetry of the laws of physics, this process of causality - which we thought only applied to the forward direction of time - in fact applies equally to the backward direction of time as well : the reason why we don ' t see causality happening in


symmetry of the laws of physics, this process of causality - which we thought only applied to the forward direction of time - in fact applies equally to the backward direction of time as well : the reason why we don ' t see causality happening in the backward direction is purely because of a bias in our psychological systems : something about the complexity of our psychological system ( our brains! ) causes our thought processes to work only in the forward direction of time ( this will be considered below ). the great advantage of recording the sequence on a movie and then playing the movie backwards ( to reveal the time symmetry of causality ) is that a movie camera works in a much more simple fashion than our brains and thus has no such psychological bias in the forward direction : it works in exactly the same way forward as backward. so if causality is time - symmetrical, we could in fact think of our current situations are being caused by time - reversed future events as much as by past events! for example, as i sit here by my desk in work this morning, i could consider my position as being caused by me being in my apartment this evening, and driving my car from there backward in time, backward down the road the work, to put me in work this morning! it ' s a bit brain - bending, but it ' s equally valid as saying " i got up this morning, and drove forwards to work ". it seems strange, but that ' s only because of our psychological bias. the movie of my complete day at work would tell the correct ( time - reversible ) story. the quantum mechanical arrow of time as has just been explained, almost all known physical principles ( from newtonian mechanics through to einstein ' s relativity ) have a completely symmetric treatment of past and future. nowhere in any of these equations is there anything which distinguishes a forward direction of time from a backward direction of time. the exception to this rule appears to be quantum mechanics. on the page on the quantum casino it was explained how, when we make a measurement of a quantum observable, there is a " collapse of the wavefunction " in which a probability wave collapses to generate a single observed value from a range of possible values. this process appears to work in the forward time direction only, i. e., it is irreversible. an explanation for this apparent " collapse of the wavefunction " is presented in detail on the page on quantum decoherence, so i don ' t want to repeat it here. suffice to


., it is irreversible. an explanation for this apparent " collapse of the wavefunction " is presented in detail on the page on quantum decoherence, so i don ' t want to repeat it here. suffice to say that the coherent phase relationships of the interference terms are destroyed when a particle interacts with the environment. the dissipation of these terms into the wider environment can be interpreted in terms of increasing entropy ( again, see the section on " decoherence and entropy " on the quantum decoherence page for full details ). quantum decoherence can then be understood as a thermodynamic process : after decoherence, the process is said to be thermodynamically irreversible. so once again the underlying physical principles appear to be time symmetric, with no fundamental preference for either the forward or backward time direction. the apparent arrow of time produced by the " collapse of the wavefunction " is once again shown to be a result of increasing entropy. as andreas albrecht explains in his paper cosmic inflation and the arrow of time ( when considering decoherence in the double - slit experiment ) : " a double - slit electron striking a photographic plate is only a good quantum measurement to the extent that the photographic plate is well constructed, and has a very low probability of re - emitting the electron in the coherent ' double slit ' state. good photographic plates are possible because of the thermodynamic arrow of time : the electron striking the plate puts the internal degrees of freedom of the plate into a higher entropy state, which is essentially impossible to reverse. furthermore, different electron positions on the plate become entangled with different states of the internal degrees of freedom, so there is essentially no interference between positions of the electron. from this point of view, the quantum mechanical arrow of time is none other than the thermodynamic arrow of time. " why can ' t we remember the future? if physical processes all appear to be time - reversible at a fundamental level, we might ask the question " why can ' t we remember the future? " after all, we can remember the past, and physics seems to make no distinction between past, present, and future. so why don ' t we already have prior knowledge of what is going to happen in the future? in order to answer this question, we shall consider the reasoning of james hartle which is based around the radiative arrow of time : the radiative arrow of time


we already have prior knowledge of what is going to happen in the future? in order to answer this question, we shall consider the reasoning of james hartle which is based around the radiative arrow of time : the radiative arrow of time in his paper the physics of " now ", james hartle makes the point that the reason we can ' t remember the future is because we have not yet received any information about future events. this thinking is based on the idea of a " light cone ", the shape of which is defined by the speed of light : at first glance, this might seem a very straightforward explanation of why we are unable to remember the future : it takes time for a light ray ( photons ) carrying information to reach us from a distant event. basically, in the future we will have more information about distant events than we have at present. it is hard to imagine a situation in which light behaves differently - it would appear that light will always take time to travel from a point a to a point b : this principle - that light will always take time, travelling forwards in time between two points - is called the radiative arrow of time ( also known as the electromagnetic arrow of time ). but this apparently clear - cut principle is not as clear - cut as it first appears. it turns out that the " world line " of the photon is the same for a photon travelling forwards in time from point a to b as it is for a photon travelling backward in time from point b to point a : in fact, if we temporarily forget about the little arrows on the world lines ( which indicate " cause " and " effect " ) then we see that the world lines of both the forward and backward photons are precisely identical : this principle is clearly illustrated by a feynman diagram of particle interactions which can be rotated at will, showing particle interactions work exactly the same backward in time as forward in time : it makes no sense to talk about the entropy of a single photon ( entropy is a statistical property of a large group of particles ), so a single photon has no arrow of time. however, we do not receive our information about distant events in the form of single photons. rather, it appears we receive information in the form of light rays which are composed of billions of photons ( bosons are quite happy to congregate in the same state, and gather together in a cooperative fashion to create light rays ). for this reason, studies of the radiative arrow of time have concentrated on


composed of billions of photons ( bosons are quite happy to congregate in the same state, and gather together in a cooperative fashion to create light rays ). for this reason, studies of the radiative arrow of time have concentrated on studying the maxwell electromagnetic field equations which treats light as a field with a wave nature ( rather than considering the path of individual particles ). it is often quoted that maxwell ' s electromagnetic field equations are time - reversible and so allow for advanced ( backward - in - time ) waves as well as retarded ( forward - in - time ) waves. however, in practice it is much easier to produce a retarded wave than an advanced wave, and this reveals the limitations of maxwell ' s equations as a full description of the behaviour of light. we need to combine maxwell ' s equations with something else in order to derive a radiative arrow of time. james hartle attempts to use maxwell ' s equations to deduce the radiative arrow of time in appendix a of his aforementioned paper the physics of " now " which is called the cosmological origin of time ' s arrow. his approach ( based on principles described in h. dieter zeh ' s book the physical basis for the direction of time ) combines the time - symmetric maxwell ' s equations with the time - asymmetric boundary conditions of the universe as a whole ( he considers the asymmetrical total amount of electromagnetic radiation ). the approach suggests that because there were no free electromagnetic fields at the start of the universe, but there are fields in the future, those fields must all be caused by retarded waves that have their sources in the past. however, i don ' t see how the radiative arrow of time can depend on the total of electromagnetic fields in the universe in this way. there ' s no equivalent of the second law of thermodynamics ( increasing entropy ) for electromagnetic fields. the total of electromagnetic field in an isolated system does not tend to increase ( as is the case with entropy ). the radiative arrow of time must surely depend on the increasing sum total of entropy in the universe, not the total of electromagnetic field. surely the radiative arrow of time must have the same cause as the thermodynamic arrow of time. at the beginning of the last century, walter ritz proposed that only retarded ( forward - in - time ) waves were physically possible ( i. e., the process was fundamentally time - asym


time. " could it be possible to remember the future? if we consider the hypothetical situation in which we have found a way to circumvent the limitations imposed by the radiative arrow of time, it is interesting to ask if it could ever be possible to remember the future. and, if so, what would our " memories " by like? in this respect, the scottish philosopher donald mackay suggested an interesting " thought experiment ". mackay wondered if it could ever be possible to predict how someone will behave in the future, and, if so, what would be the consequences for human free will. if we had complete knowledge of the current state of a person ' s brain, would we be able to accurately predict a person ' s actions in the short - term future? basically, if we are able to predict how a person will behave - and the decisions they will make - in the future then human free will is shown to be a fallacy, an illusion. however, mackay suggested that it would be impossible to predict a person ' s future decisions if that predicted future was made known to the person. this is because the person could then choose to act in a different way from how you have told him he will behave. this is described by john d. barrow in his book impossibility : " consider a person who is asked to choose between soup or salad for lunch. if we introduce a brain scientist who not only knows the complete state of this person ' s brain, but that of the entire universe as well at present, we could ask whether this scientist can infallibly announce what the choice of lunch will be. the answer is ' no '. the subject can always be stubborn, and adopt a strategy that says ' if you say that i will choose soup, then i will choose salad, and vice versa '. under these conditions it is logically impossible for the scientist to predict infallibly what the person will choose if the scientist makes his prediction known. " so if a person gains access to knowledge about his future behaviour, it would appear that it becomes impossible to predict that future. but this knowledge about future behaviour is precisely what a person will gain if he is able to remember the future. so if a person is able to remember the future, he could then choose to act in a different way to how his memory of the future tells him he will act! there would appear to be a logical inconsistency here : if a person is able to remember the future, then those memories of the future instantly become


an animal detection system with the warning lights activated resulted in 1. 52 mi / h lower vehicle speeds ( compared to warning lights off ) for passenger cars and pick - ups. alerting drivers to the presence of large animals in the road at yellowstone national park. the study area was on us highway 191 inside of the yellowstone national park, with a posted speed limit of 55 mi / hour. the data collection period occurred over two weeks in which there was mostly no precipitation. researchers installed three traffic counters and road tubes outside and inside of the detection area. the counters recorded the date, time, vehicle type, vehicle speed and gap ( in seconds ) between vehicles. when vehicles moved in platoons, only the speed of the first vehicle in a platoon was used as a data point when the signs were activated ( since the following vehicles may be influenced by the speed of the first one ). a sample size of 2, 428 vehicles per 24 hour period was used. the deployment of an animal detection system at yellowstone national park found that passenger cars, pick - ups, vans, and trucks with two units or more had lower vehicle speeds by 1. 52 mi / hour with warning signs activated compared to warning signs off. although the difference is small, it is important to note that small reductions when vehicles are traveling at high speeds have a disproportionate decrease in the probability of severe accidents. the data also showed that the number of collisions with large animals was 58 to 67 percent lower than was expected ( but could not be tested for significance due to the variability in the number of collisions and just one year of post installation collision data ). driver opinion of the system documented in interviews revealed that a majority ( 59 percent ) would have liked to see the system stay in place. the system was removed in the fall of 2008 due to high maintenance and a lack of spare parts. author : m. p. huijser, t. d. holland, a. v. kociolek, a. m. barkdoll and j. d. schwalm published by : oregon department of transportation research unit and the federal highway administration source date : march 2009url : http : / / ntl. bts. gov / lib / 31000 / 31600 / 31698 / animal - vehicle _ crash _ mitigation _ phase _ 2. pdf average user rating typical deployment locations


waste is defined as something that is unwanted or unusable. according to the office of national statistics, a staggering 342m tonnes of waste is produced in the uk each year. instead of going to landfill sites to be buried or burnt, a vast proportion of this waste could be cut using the following steps : reduce – change manufacturing processes so that less materials are used or change consumer habits so that less wasted material is bought reuse – choose goods and products that can be used again and reuse rubbish for other purposes recycle – make sure that waste is processed and made into another product wherever possible. composting is also recycling : the nutrients in organic waste are processed and returned to the soil to help more plants to grow reducing your waste any building or environment where people live or work will produce a certain amount of waste, and children ’ s centres are no exception. reducing waste may involve taking an in - depth look at the types of resources your centre buys and considering ways of cutting down. there are numerous ways a children ’ s centre can reduce the amount of waste produced and handle waste in a more environmentally friendly way. does the centre recycle and, if so, what types of waste do you recycle? could you recycle more or re - use materials such as paper and yoghurt pots? instead of paying companies to remove your waste, by recycling it you will save money in the long - term as you won ’ t need to pay contractors to take it away. you may also be able to sell some of your metal and glass to companies who can recycle it. ensure that paper recycling bins are placed in every classroom and discuss with the children what they are and why they are needed. encourage children to use both sides of paper and when they ’ re finished to use the recycling bins. composting is a great way of disposing of food waste in an environmentally friendly way. place compost bins around the centre grounds and ask the children to help empty the food into the bins. children could then draw pictures of the different foods which are composted. ask children to look into their lunch box and identify what waste can be composted and what can ’ t. explain how certain items such as yoghurt pots can be re - used to make paint pots etc. visit our resources & links to download a rupert bear themed waste dot to dot activity. this section also provides details of organisations that will be able to help your centre tackle the waste topic.


click here for an introduction to some basic concepts and design principles of secret key cryptography. 3 - way is a simple and fast cipher designed by joan daemen. 3 - way features a 96 - bit key length and a 96 - bit block length. 3 - way is an iterated block cipher that repeats some relatively simple operations a specified number of rounds. david wagner, john kelsey, and bruce schneier of counterpane systems have discovered a related key attack on 3 - way that requires one related key query and about 222 chosen plaintexts, described in this paper. 3 - way is unpatented. blowfish is a block cipher designed by bruce schneier, author of applied cryptography. blowfish combines a feistel network, key - dependent s - boxes, and a non - invertible f function to create what is perhaps one of the most secure algorithms available. schneier ' s paper is available is also described in the concepts of cryptography page. the only known attacks against blowfish are based on its weak blowfish is implemented in kremlin. cast, designed by carlisle adams and stafford taveres, is shaping up to be a solid algorithm. its design is very similar to blowfish ' s, with key - dependent s - boxes, a non - invertible f function, and a feistel network - like structure ( called a substitution - permutation network ). david wagner, john kelsey, and bruce schneier have discovered a related - key attack on the 64 - bit version of cast that requires approximately 217 chosen plaintexts, one related query, and 248 offline computations ( described in this paper ). the attack is infeasible at best. cast is patented by entrust technologies, which has generously released it for free use. the cast cipher design process is described in this paper and the 128 - bit version is described in this addendum. carlisle adams has submitted a version of cast ( cast - 256 ) as an aes candidate. cast - 128 is implemented in kremlin. cmea is the encryption algorithm developed by the telecommunications industry association to encrypt digital cellular phone data. it uses a 64 - bit key and features a variable block length. cmea is used to encrypt the control channel of cellular phones. it is distinct from oryx, an also insecure stream cipher that is used to encrypt data transmitted over digital cellular phones. it has been


block length. cmea is used to encrypt the control channel of cellular phones. it is distinct from oryx, an also insecure stream cipher that is used to encrypt data transmitted over digital cellular phones. it has been broken by david wagner, john kelsey, and bruce schneier of counterpane systems. their paper, which also provides an excellent description of the cmea algorithm, is available here. designed at ibm during the 1970s and officially adopted as the nist standard encryption algorithm for unclassified data in 1976, des has become the bastion of the cryptography market. however, des has since become outdated, its long reign as official nist algorithm ending in 1997. though des accepts a 64 - bit key, the key setup routines effectively discard 8 bits, giving des a 56 - bit effective keylength. des remains widely in use. during the design of des, the nsa provided secret s - boxes. after differential cryptanalysis had been discovered outside the closed fortress of the nsa, it was revealed that the des s - boxes were designed to be resistant against differential cryptanalysis. des is becoming weaker and weaker over time ; modern computing power is fast approaching the computational horsepower needed to easily crack des was designed to be implemented only in hardware, and is therefore extremely slow in software. a recent successful effort to crack des took several thousand computers several months. the eff has sponsored the development of a crypto chip named " deep crack " that can process 88 billion des keys per second and has successfully cracked 56 bit des in less than 3 days. des is implemented in kremlin ( accessible through kremlin sdk api ). a variant of des, triple - des ( also 3des ) is based on using des three times. this means that the input data is encrypted three times. the triple - des is considered much stronger than des, however, it is rather slow compared to some new block ciphers. deal is an interesting aes submission and, like all aes submissions, it uses a 128 bit block and accepts 128 bit, 192 bit, and 256 bit keylengths. it uses des as its inner round function and its authors suggest at least 6, preferably 8 rounds ( there are some attacks against deal ). there is a paper available here that describes some attacks, all of which can be cured by using at least developed by the nippon telephone & telegraph as an improvement to des, the fast data encipherment algorithm ( feal )


against deal ). there is a paper available here that describes some attacks, all of which can be cured by using at least developed by the nippon telephone & telegraph as an improvement to des, the fast data encipherment algorithm ( feal ) is very insecure. feal - 4, feal - 8, and feal - n are all susceptible to a variety of cryptanalytic attacks, some requiring as little as 12 chosen plaintexts. feal is patented. gost is a cryptographic algorithm from russia that appears to be the russian analog to des both politically and technologically. its designers took no chances, iterating the gost algorithm for 32 rounds and using a 256 bit key. although gost ' s conservative design inspires confidence, john kelsey has discovered a key - relation attack on gost, described in a post to sci. crypt on 10 february 1996. there are also weak keys in gost, but there are too few to be a problem when gost is used with its standard set of s - boxes. you can read the official gost algorithm description ( translated from russian ) here. there is also a description of the gost algorithm here. idea, developed in zurich, switzerland by xuejia lai and james massey, is generally regarded to be one of the best and most secure block algorithm available to the public today. it utilizes a 128 - bit key and is designed to be resistant to differential cryptanalysis. some attacks have been made against reduced round idea. unfortunately, idea is patented ; licensing information can be obtained from ascom. loki was designed as a possible replacement for des. it operates on a 64 - bit block and a 64 - bit key. the first version of loki to be released was broken by differential cryptanalysis and was shown to have an 8 - bit complementation property ( this means that the number of keys that need to be searched in a brute force attack is reduced by 256 ). loki was revised and re - released as loki91. loki91 is secure against differential cryptanalysis, but loki easily falls to a chosen - key attack. the designers of loki have proposed loki97 as an aes candidate, but linear and differential attacks on loki97 have already been proposed. lucifer was one of the first modern cryptographic algorithms. it was designed at ibm in the 1960s by horst feistel, of feistel network fame. lucifer is often considered to be a precursor to des. there are several incarnations of lucifer, each with the


the first modern cryptographic algorithms. it was designed at ibm in the 1960s by horst feistel, of feistel network fame. lucifer is often considered to be a precursor to des. there are several incarnations of lucifer, each with the same name, which creates a good deal of confusion. no version is secure. a paper on the differential cryptanlysis of lucifer was written by ishai ben - aroya & eli macguffin is a cipher developed by matt blaze and bruce schneier as an experiment in cipher design. it uses a feistel network ( see the cryptography overview for details ), but does not split the input evenly, instead dividing the 64 bit block into one 16 bit part and another 48 bit part. this is called a generalized unbalanced feistel network ( gufn ). details are available here. a differential attack on macguffin has been found that requires approximately 251. 5 chosen plaintexts. mars is ibm ' s aes submission. there is a mars web page with a link to the mars paper. mars uses 128 bit blocks and supports variable key sizes ( from 128 to 1248 bits ). mars is unique in that it combines virtually every design technique known to cryptographers in one algorithm. it uses addition and subtractions, s - boxes, fixed and data dependent rotations, misty is a cryptographic algorithm developed by mitsubishi electric after they broke des in 1994. it is designed to withstand linear and differential cryptanalysis, but has not yet been cryptanalysed. as it has not undergone intensive peer review, the usual caution is recommended. it is being considered for inclusion into the set 2. 0 standard. visit web page or read the author ' s paper mmb was designed as an alternative to idea that uses a 128 - bit block instead of idea ' s 64 - bit block. it was designed using the same principles as idea. unfortunately, it is not as secure as idea and several attacks exist against it. its author, joan daemen, abandoned it and designed although newdes was developed by robert scott to possibly replace des, newdes has fallen short of expectations. newdes has been proven to be weaker than des, requiring 24 related - key probes and 530 chosen plaintext / ciphertext queries, as described in this newdes is implemented in kremlin rc2, like rc4, was formerly a trade secret, but code purporting to be rc2 was posted to sci. crypt. it is


/ ciphertext queries, as described in this newdes is implemented in kremlin rc2, like rc4, was formerly a trade secret, but code purporting to be rc2 was posted to sci. crypt. it is archived here. david wagner, john kelsey, and bruce schneier discovered a related - key attack on rc2 that requires one related - key query and approximately 234 chosen plaintexts. rc2 is not patented by rsa data security, inc ; it is just protected as a trade secret. rc5 is a group of algorithms designed by ron rivest of rsa data security that can take on a variable block size, key size, and number of rounds. the block size is generally dependent on the word size of the machine the particular version of rc5 was designed to run on ; on 32 - bit processors ( with 32 - bit words ), rc5 generally has a 64 - bit block size. david wagner, john kelsey, and bruce schneier have found weak keys in rc5, with the probability of selecting a weak key to be 2 - 10r, where r is the number of rounds. for sufficiently large r values ( greater than 10 ), this is not a problem as long as you are not trying to build a hash function based on rc5. kundsen has also found a differential attack on rc5. rc5 is described in this rsa document. rc5 is patented by rsa rc6 is ronald rivest ' s aes submission. like all aes ciphers, rc6 works on 128 bit blocks. it can accept variable length keys. it is very similar to rc5, incorporating the results of various studies on rc5 to improve the algorithm. the studies of rc5 found that not all bits of data are used to determine the rotation amount ( rotation is used extensively in rc5 ) ; rc6 uses multiplication to determine the rotation amount and uses all bits of input data to determine the rotation amount, strengthening the avalanche effect. there are two versions of the redoc algorithm, redoc ii, and redoc iii. redoc ii is considered to be secure ; an attack has been made against one round of redoc ii, but could not be extended to all 10 recommended rounds. redoc ii is interesting in that it uses data masks to select the values in the s - boxes. redoc ii uses a 160 - bit key and works on an 80 - bit block. redoc iii was an attempt to


10 recommended rounds. redoc ii is interesting in that it uses data masks to select the values in the s - boxes. redoc ii uses a 160 - bit key and works on an 80 - bit block. redoc iii was an attempt to make the painfully slow redoc ii faster. redoc iii, like redoc iii, operates on an 80 - bit block, but can accept keys up to 20480 bits. however, redoc iii falls to differential cryptanalysis, as described in this rijndael is an aes winner by joan daemen and vincent rijmen. the cipher has a variable block and key length, and the authors have demonstrated how to extend the block length and key length by multiples of 32 bits. the design of rijndael was influenced by the square algorithm. the authors provide a rijndael specification and a more theoretical paper on their design principles. the authors have vowed to never patent rijndael. safer was developed by robert massey at the request of cylink corporation. there are several different versions of safer, with 40, 64, and 128 - bit keys. a weakness in the key schedule was corrected, with an s being added to the original safer k designation to create safer sk. there are some attacks against reduced round variants of safer. safer is secure against differential and linear cryptanalysis. however, bruce schneier, author of applied cryptography, recommends against using safer because, " safer was designed for cylink, and cylink is tainted by the nsa. " safer sk - 128 is implemented in kremlin. serpent is an aes submission by ross anderson, eli biham, and lars knudsen. its authors combined the design principles of des with the recent development of bitslicing techniques to create a very secure and very fast algorithm. while bitslicing is generally used to encrypt multiple blocks in parallel, the designers of serpent have embraced the technique of bitslicing and incorporated it into the design of the algorithm itself. serpent uses 128 bit blocks and 256 bit keys. like des, serpent includes an initial and final permutation of no cryptographic significance ; these permutations are used to optimize the data before encryption. serpent was released at the 5th international workshop on fast software encryption. this iteration of serpent was called serpent 0 and used the original des s - boxes. after comments, the key schedule of sperpent was changed slightly and the s - boxes were changed ; this new iteration of serpent


workshop on fast software encryption. this iteration of serpent was called serpent 0 and used the original des s - boxes. after comments, the key schedule of sperpent was changed slightly and the s - boxes were changed ; this new iteration of serpent is called serpent 1. serpent 1 resists both linear and differential attacks. the serpent paper is available here. square is an iterated block cipher that uses a 128 - bit key length and a 128 - bit block length. the round function of square is composed of four transformations : a linear transformation, a nonlinear transformation, a byte permutation, and a bitwise round - key addition. square was designed to be resistant to linear and differential cryptanalysis, and succeeds in this respect. the designers of square have developed an attack on square, but it cannot be extended past 6 rounds. a paper on square is and there are links to the paper and source code on the designers ' web in what surely signals the end of the clipper chip project, the nsa released skipjack, its formerly secret encryption algorithm, to the public. skipjack uses an 80 bit key. a fuzzy scan of the official nsa paper is available here at the nist web site, but it has been transcribed by the folks over at jya. com. a reference implementation ( in c ) is available here, and an optimized version is available here. eli biham and adi shamir have published some initial cryptanalytic results ( which are growing more and more interesting as time progresses ). tiny encryption algorithm ( tea ) tea is a cryptographic algorithm designed to minimize memory footprint, and maximize speed. however, the cryptographers from counterpane systems have discovered three related - key attacks on tea, the best of which requires only 223 chosen plaintexts and one related key query. the problems arise from the overly simple key schedule. each tea key can be found to have three other equivalent keys, as described in a paper by david wagner, john kelsey, and bruce schneier. this precludes the possibility of using tea as a hash function. roger needham and david wheeler have proposed extensions to tea that counter the above attacks. twofish is counterpane systems ' aes submission. designed by the counterpane team ( bruce schneier, john kelsey, doug whiting, david wagner, chris hall, and niels ferguson ), twofish has undergone extensive analysis by the counterpane team. there is a paper available from the twofish web page and source


. sha1 is similar in design to md4. the original published algorithm, known as sha, was modified by nsa to protect against an unspecified attack ; the updated algorithm is named sha1. it produces a 160 - bit digest - - large enough to protect against " birthday " attacks, where two different messages are selected to produce the same signature, for the next decade. the official fips description of sha1 can be found sha1 is implemented in kremlin. snefru is a hash function designed by ralph merkle, the designer of the khufu and khafre encryption algorithms. 2 - round snefru has been broken by eli biham. snefru 2. 5, the latest edition of the hash algorithm, can generate either a 128 - bit or a 256 - bit digest. tiger is a new hash algorithm by ross anderson and eli biham. it is designed to work with 64 - bit processors such as the digital alpha and, unlike md4, does not rely on rotations ( the alpha has no such rotate instruction ). in order to provide drop - in compatibility with other hashes, tiger can generate a 128 - bit, a 160 - bit or a 192 - bit digest. the tiger home page contains more information. want to add to the list of algorithms ( or found a mistake )? please


atp hydrolysis in f1 - atpase why is f1fo - atp synthase so important? f1fo - atp synthase, or atp synthase for short, is one of the most abundant proteins in every organism. it is responsible for synthesizing the molecule adenosine tri - phosphate ( atp ), the cells ’ energy currency. atp is depicted in fig. 1 and used to power and sustain virtually all cellular processes needed to survive and reproduce. even when at rest, the human body metabolizes more than half its body weight in atp per day, this figure rising to many times the body weight under conditions of physical activity. what do we know about f1fo - atp synthase? researchers have been trying to uncover the " secret " behind atp synthase ’ s very efficient mode of operation for quite some time. unfortunately, even after more than 30 years of study, we still don ’ t fully understand how f1fo - atpase really works. the protein consists of two coupled rotary molecular motors, called fo and f1, respectively, the first one being membrane embedded and the latter one being solvent exposed. one of the most important breakthroughs in the field was the determination of an atomic resolution x - ray crystal structure for the f1 part of atp synthase. this allowed researchers, for the first time, to connect biochemical data to the three dimensional structure of the protein ( abrahams et al., nature 370 : 621 - 628, 1994 ). the x - ray structure beautifully supported paul boyer ’ s " binding change mechanism " ( boyer, bioch. bioph. acta 215 - 250, 1993 ) as the modus operandi for atp synthase ’ s rotational catalytic cycle and lead to the 1997 nobel prize in chemistry for boyer and walker. f1 - atpase in its simplest prokaryotic form ( shown schematically in fig. 2 ) consists of a hexameric assembly of alternating α and β subunits arranged in the shape of an orange. the central cavity of the hexamer is occupied by the central stalk formed by subunits γ, δ and ε. due to a lack of high resolution structures for the fo part of atp synthase, much less is known about this subunit. it is currently thought that a transmembrane proton gradient drives rotation of the c - subunit ring of fo which is then coupled to movement of the central stalk. the rotation of the latter eventually causes conformational changes in the catalytic sites located in f1 leading to the synthesis of atp


and the catalytic core region as well as several computational mutation studies identified the " arginine finger " residue αr373 as the most significant element involved in this change in energetics. several important conclusions can be drawn from our simulations : efficient catalysis proceeds via a multi - center proton pathway and a major factor for atpase ’ s efficiency is, therefore, the ability to provide the proper solvent environment by means of its catalytic binding pocket. furthermore, the sidechain of the arginine finger residue αr373 is found to be a major element in signaling between catalytic sites to enforce cooperation since it controls the reaction barrier height as well as the reaction equilibrium of the atp hydrolysis / synthesis reaction. zooming in on atp hydrolysis in f1. markus dittrich and klaus schulten. journal of bioenergetics and biomembranes, 37 : 441 - 444, 2005. atp hydrolysis in the btp and bdp catalytic sites of f1 - atpase. markus dittrich, shigehiko hayashi, and klaus schulten. biophysical journal, 87 : 2954 - 2967, 2004. on the mechanism of atp hydrolysis in f1 - atpase. markus dittrich, shigehiko hayashi, and klaus schulten. biophysical journal, 85 : 2253 - 2266, 2003. other qm / mm projects this material is based upon work supported by the national science foundation under grant no. 0234938. any opinions, findings, and conclusions or recommendations expressed in this material are those of the author ( s ) and do not necessarily reflect the views of the national science foundation.


what it means for you if you follow discussions about the rising costs of serials or the “ crisis ” in scholarly communication, you may have heard the term “ open access ” applied to either journals or publishing in general. and if you are like many people, you can barely keep up with developments in your field, let alone those that may be considered tangential. this article will explain the open access publishing model, and help you understand why it matters to you and how you can participate. open access refers to a publication that meets two conditions according to the bethesda statement on open access publishing. the first condition is that the author ( s ) and / or copyright holder ( s ) of an article grants all readers “ free, irrevocable, worldwide, perpetual right of access ” to the article as well as the right to “ distribute, transmit and display ” the work with proper attribution of authorship. the second condition is that a complete version of the article be included in a stable online repository set up for the purpose of enabling open access. open access can be the property of an individual article or it can be the policy of a specific journal. in plain language, this means that the authors retain copyrights to their work, so that no second or third party may profit from it, and the work immediately goes into a publicly accessible archive. the goal of the open access movement is to decrease the obstacles between the discovery of scientific information and the application of it to our lives. under the traditional model of publishing, scientific discoveries were published in journals owned and operated by outside parties, who then assumed all copyrights to the articles, and could turn around and profit from them. based on the traditional model, publishers were able to profit from the research of the scientific community by essentially charging scientists for access to their own work via library subscriptions. during the 1980 ’ s and 1990 ’ s, the publishing industry experienced significant consolidation through a flurry of corporate mergers. the result of this was not only diminished diversity in the marketplace, but inflation in journal prices. for example, in 1991 reed - elsevier acquired pergamon, which resulted in a 10 percent price increase for reed - elsevier journals. similar increases have been documented in relation to other mergers. most striking, however, is the fact that between 1986 and 2000 inflation rates for journal subscriptions surpassed that of both college tuition and medical care! inflation in journal prices ultimately sucked money away from other areas of the library budget ; students and faculty suffered as librarians made excruciating decisions


what is chiropractic treatment? is an alternative medicine to treat back pain through manipulation of the spine. chiropractic technique involves use of the practitioners ’ hands to press, pull and otherwise adjust the spine, neck, joints and surrounding soft tissues. spinal manipulation is thought to correct misaligned vertebrae, helping lessen back pain and reduce muscle spasms. insurance companies typically cover visits to the chiropractor. the hypothesis behind how chiropractic treatment works maintains that disorders of the spine adversely affect overall health and that chiropractic can help improve overall health. however, no evidence has conclusively proven this hypothesis. chiropractors believe the vertebra becomes out of normal alignment, which interferes with the nervous system. this misalignment is called “ subluxation. ” the u. s. agency for health care policy and research recognizes chiropractic treatment as being effective for lower back pain. who are chiropractors and what do they do? chiropractors are health professionals who diagnose, treat and seek to prevent spine disorders or back pain. chiropractors are considered part of the alternative health care field and focus on improving patients ’ health and well - being without resorting to drugs or surgery. chiropractic treatment typically includes not only spinal manipulation, but also a regimen of exercise and counseling about health and lifestyle. chiropractors typically attend college for a bachelor ’ s degree – or obtain a two - year degree – and attend four postgraduate years in a doctor of chiropractic school. the last year of school, students practice chiropractic techniques while being supervised. students graduate as doctors of chiropractic ( d. c. ). some states require additional exams to practice. some chiropractors focus on musculoskeletal adjustments, while others are also trained in physical therapy, electrical stimulation, soft - tissue therapy and ultrasound. what should i expect during an initial chiropractor appointment? a first visit to a chiropractor takes an hour or longer. the chiropractor will compile a complete medical history and may perform tests, such as x - rays, mris or neurological tests. once a problem is detected, subsequent visits to a chiropractor typically take a few minutes to complete the spinal manipulations and adjustments. from appointment to appointment, a chiropractor will monitor changes in a patient ’ s spine and level of back pain using tests, observation,


| vii. why is the progress of evolution cyclic? question is one which necessarily appalls us and makes us wonder. let us, therefore, deal with it as follows : certain ideas are involved in the thought of cyclic progression, and these ideas it might pay us well to contemplate. 1. the idea of repetition this repetition involves the following factors : - repetition in time : the thought of cyclic activity necessitates periods of time of differing length - greater or lesser cycles - but ( according to their length ) of uniform degree. a manvantara, or day of brahma, is always of a certain length, and so is a mahamanvantara. the cycles wherein an atom of any plane revolves upon its axis are uniform on its own plane. - repetition in fact : this involves the idea of a key measure, or sound of any particular group of atoms that go to the composition of any particular form. this grouping of atoms will tend to the makeup of a particular series of circumstances and will repeat the measure or sound when an animating factor is brought to bear upon them. when the vitalizing force is contacting at stated periods a certain set of atoms, it will call forth from them a specific sound which will demonstrate objectively as environing circumstances. in other words, the interplay of the self and the not - self is invariably of a cyclic nature. the same quality in tone will be called forth by the self as it indwells the form, but the key will ascend by gradual degrees. it is similar to the effect produced in striking the same note in different octaves, beginning at the base. - repetition in space : this concept is involved deep in the greater concept of karma, which is really the law that governs the matter of the solar system, and which commenced its work in earlier solar systems. we have, therefore, cycles in order, and repetition in an ever - ascending spiral, under definite law. the thoughts thus conveyed might be expressed likewise as follows : chain repeating its activity - repetition in time. consecutive reverberation of a plane note, of a subplane note, and of all that is called into objectivity by that note - plane repetition. of atoms to perpetuate their activity, and thus produce similarity of circumstance, of environment, and of vehicle - form repetition. - the solar system repeating its activity - repetition in space. carry these ideas on to every plane in the solar system, and from thence to the cosmic planes, we have opened up for


cancer cells in bloodstream show great diversity : study tuesday, may 8 ( healthday news ) - - there is a great deal of genetic diversity in cells shed by cancerous tumors into the bloodstream, a new study has found. some cells have genes that enable them to lodge themselves in new locations, helping the cancer spread between organs, while other cells have different patterns of gene expression that might make them more benign or less likely to survive in other locations in the body. some circulating tumor cells even express genes that could predict their response to a specific cancer treatment, the researchers said. " within a single blood draw from a single patient, we ' re seeing [ varied ] populations of circulating tumor cells, " senior study author dr. stefanie jeffrey, chief of surgical oncology research at the stanford university school of medicine, said in a university news release. the researchers said their findings highlight how multiple types of treatment may be needed to cure what appears to be a single kind of cancer and suggest that the current cell - line models of human cancers need to be improved upon. the study, which used blood samples from breast cancer patients, is the first to look at circulating tumor cells one by one instead of taking the average of many of the cells. it also is the first to show the extent of genetic differences between circulating tumor cells, the researchers said. scientists have long known that circulating tumor cells move through the bloodstreams of cancer patients. over the past five years, though, many cancer researchers have begun to think the cells could be the key to tracking tumors noninvasively. the study appears online tuesday in the journal plos one. the u. s. national cancer institute has more about cancer. source : stanford university, news release, may 7, 2012


the previous discussion of entertainment as a world paradigm only hinted at the origin of that paradigm. more to the point, it dabbled in connections between music as art and entertainment, and suggested that such a duality could be relatively recent in origin. in some sense, this distinction is about upper - and lower - class activity, and the simplest historical narrative involves a flip - flop of power between the two. in the current economic climate, the lower classes, by virtue of number ( i. e. democracy ), have achieved " artistic " control. one can construct a basic linear progression of this type, from the utter dominance of ancient tyrants to the mass - market politics of today. a progression of that sort can be rather illuminating with regard to the balancing act which established the classical style. however, such a naive progression makes a basic underlying assumption, namely that popular music of earlier centuries was rather distinct from — even contemptuous of, as it is today — elite music. in fact, many people take very strong views on this point, related especially to what they retrospectively view as religious & other oppression. they are certain, often on whim alone, that a lively & distinct popular culture existed in the medieval era, and might even ( paradoxically ) associate some surviving songs with it. they reconstruct today ' s divisions in their minds. fundamentally, the survival of sources is about writing, an elite activity, so that associations with a distinct popular culture can only be considered fanciful — at least insofar as one presumes a distinct or even hostile relation. what sort of historical relation can we find between " popular " & elite music? moreover, can we trace art - or entertainment - based musical priorities? any answers must be fairly tentative, given the relative lack of information. working backward in time somewhat to the fringe of the modern era, we know that sacred & secular music intermingled closely. themes — even forms themselves — were freely borrowed in the franco - flemish era. i have immediately side - stepped some important terminological concerns, by introducing a sacred - secular juxtaposition. we have no real reason to believe that the polyphonic courtly chanson was related to what we would recognize as popular music today. however, this era also presents us with the survival of manuscripts ( bayeux, say ) which we conclude to have represented the popular music of the time. these themes then intermingle directly in courtly secular and sacred music. as near as we can believe, and by the 1500s


however, all indications are that there was less distinction between music for entertainment and music for ritual. speculating about prehistory, the mere act of creating a song must have been cathartic, as vocal ritual helped to tame the psychological traumas of nature. the courtly love song was created as a sort of ritual, albeit a non - or even anti - religious one. from there, we find some evidence of intellectual divergence in the church ' s protestations regarding increasingly elaborate ars nova liturgical music. presumably there were conservative theologians at several points in medieval history who frowned upon a new artistic license entering the domain of sacred music. nonetheless, if nothing else, surviving protestations prove that these concerns were frequently combined, even as their differing goals were prescribed. again returning to a fifteenth century orientation, sacred works made heavy use of secular ( art ) material. ritual mixed closely with art. to return to our underlying question, given uncertainties regarding earlier eras, we cannot necessarily know if there was a divergence between art & entertainment, but nonetheless i will accept that there was not, and look for such a bifurcation in the modern era. at the very least, one can reasonably suppose that there was a bifurcation after the 1500s. the more unsteady distinction in those earlier eras was between sacred & secular music. one might even hypothesize that ritual music was the basic stuff of lower - class music - making before the arrival of secular literature, seeing as it was intended to provide protection from the hazards of the world. communion was a real need. from this point of extreme historical uncertainty on our part, there are various points at which sacred & secular music - making seem more or less close — a cyclical pattern which maintained after the 1500s as well, with differing religious or artistic movements sometimes increasing or decreasing that distance. today we cannot necessarily separate art and religious music. for the most part, though, we can separate them from entertainment, at least as i have contrasted aesthetic & entertainment paradigms. jumping ahead from the fifteenth to the eighteenth century, we can again observe clearly that music for art & music for entertainment operated in the same space, indeed were basically interchangeable. so the bifurcation we seek did not occur until the establishment of the composer as supreme alongside the distinct popular markets of the nineteenth century, and was not consummated until the unprecedented technological revolution of the twentieth. with it, we see bifurcations of complexity, masterpieces, and then the dissolution of a mainstream reference


boston, dec. 19 - - an experimental lab - on - a - chip can accurately detect cancer cells circulating in the blood, researchers here said. the chip - - slightly more than 1. 5 square inches in area - - detected circulating cancer cells in 115 of 116 blood samples from patients with metastatic cancer for a sensitivity of 99. 1 %, according to daniel haber, m. d., director of the massachusetts general hospital cancer center, and colleagues. and it found no cancer cells in the blood of healthy volunteers, for a specificity of 100 %, the researchers reported in the dec. 20 issue of nature. " clearly this has tremendous potential for early diagnosis, " dr. haber said, but it also has the potential to allow physicians to monitor the success or failure of treatment more closely and to begin to solve some of the puzzles that surround metastasis. circulating tumor cells are found in patients even before a cancer has begun to spread, but they are rare - - as few as one in a billion hematologic cells even in the metastatic case - - and hard to isolate, the researchers said. current approaches use complicated analytic techniques - - including centrifuging and washing samples - - that generate very low yield and purity, they said. in contrast, their " microfluidics " approach is highly sensitive, has a 99 % yield, and a purity approaching 50 %, compared with less than 1 % for other methods, the researchers said. the development of the chip " bring [ s ] us closer to having a fully automated instrument that can detect circulating tumor cells with exquisite sensitivity, " said jonathan uhr, m. d., of the university of texas southwestern medical center in dallas, writing in an accompanying comment. dr. uhr said such a device " would allow routine monitoring of blood for tumor cells as part of a medical examination, and could result in early detection and treatment. " the researchers said that a number of engineering challenges remain before the system can be used for clinical applications, although it could be used now for research. microchips have been used for a range of analytic chores, such as flow cytometry, but have not been applied to tasks where milliliter - sized samples of whole blood must be analyzed, he and colleagues noted. on theoretical grounds, they concluded that a microchip array of 78, 000 tiny silicon posts - - coated with an antibody to a molecule specific to tumor cells - - would overcome that barrier. the posts were coated with an antibody


and colleagues noted. on theoretical grounds, they concluded that a microchip array of 78, 000 tiny silicon posts - - coated with an antibody to a molecule specific to tumor cells - - would overcome that barrier. the posts were coated with an antibody to anti - epithelial - cell adhesion - molecule, or epcam, which is found on tumor cells, but not on blood cells. tests showed that when the researchers processed blood samples spiked with tumor cells, the epcam - coated posts captured them easily, although the posts also captured some white blood cells. to test the chip in the real world, the researchers tested 116 blood samples from 68 patients with metastatic epithelial cancers including non - small - cell lung, prostate, pancreatic, breast, and colon, as well as 20 samples from healthy volunteers. except for one sample that was smaller than average - - 0. 9 milliliters compared with 2. 7 milliliters - - the system found circulating tumor cells in all samples from patients, but none in the samples from healthy volunteers. in addition, circulating tumor cells were isolated in seven out of seven patients with early - stage prostate cancer. in a separate analysis, dr. haber and colleagues tested sequential samples from nine patients undergoing treatment and found that the percentage change in the number of tumor cells they captured correlated well with percentage change in tumor size. ( the pearson ' s correlation coefficient was 0. 68, which was significant at p = 0. 03. ) " much of cancer [ drug ] treatment now is trial and error, " dr. haber said. the chip might potentially allow doctors to find the correct treatment more quickly. one advantage of the system, dr. haber said, is that captured cells remain alive, opening the door to more detailed understanding of how they function and perhaps what causes some to become the root of new cancers while the majority commit cell suicide. " we ' d like to study exactly what they are, " he said. | the study was supported by the nih and a doris duke distinguished clinical scientist award. dr. haber reported no conflicts. | primary source : nature nagrath s, et al " isolation of rare circulating tumour cells in cancer patients by microchip technology " nature 2007 ; 450 : 1235 - 41.


definition of aging aging : the process of becoming older, a process that is genetically determined and environmentally modulated. research into aging : to sum up the state of research into aging is well beyond the confines of this space ( and this writer ' s talents ). however, here is one type of research into the genetics of aging. a gene has been discovered that helps determine the life - span of the fruit fly drosophila. when the gene is mutated ( altered ), it can extend the life - span of fruit flies. it doubles their life - span. the gene has been named indy ( for i ' m not dead yet ). it appears that the protein encoded by this gene transports and recycles metabolic byproducts. defects in the gene may lead to production of a protein that renders metabolism less efficient so that its body functions as if the fruit fly were dieting, even though its eating habits are unchanged. mutations in indy thus appear to create a metabolic state that mimics caloric restriction, which has been shown to extend life - span. reference : rogina b, reenan ra, nilsen sp, and helfand sl. extended life - span conferred by cotransporter gene mutations in drosophila. science dec 15 2000 : 2137 - 2140. some useful suggestions for extending life : no known substance can halt aging or extend life, but here are some useful tips for improving the chances of living a long time and staying healthy : last editorial review : 6 / 14 / 2012 back to medterms online medical dictionary a - z list need help identifying pills and medications? get the latest health and medical information delivered direct to your inbox free!


a group of individuals agreeing in common attributes, and designated by a common name ; a conception subordinated to another conception, called a genus, or generic conception, from which it differs in containing or comprehending more attributes, and extending to fewer individuals. thus, man is a species, under animal as a genus ; and man, in its turn, may be regarded as a genus with respect to european, american, or the like, as species. in science, a more or less permanent group of existing things or beings, associated according to attributes, or properties determined by scientific observation. a sort ; a kind ; a variety ; as, a species of low cunning ; a species of generosity ; a species of cloth. an officinal mixture or compound powder of any kind ; esp., one used for making an aromatic tea or tisane ; a tea mixture. a group of living things that appear to have common ancestry so closely related that their characteristics definitely separate them all from any other group ; a further division of a genus. n. ( l. species, particular kind ) a group of interbreeding individuals, not interbreeding with another such group, being a taxonomic unit including two names in binomial nomenclature, the generic name and specific epithet, similar and related species being grouped into a genus. a group of organisms that differ from all other groups of organisms and that are capable of breeding and producing fertile offspring. this is the smallest unit of classification for plants and animals. a group of closely related plants under the same genus. the lowest group of creatures in the tree of life. the hierarchy is as follows : kingdom ; phylum ; class ; order ; family ; genus ; species. the species is the group of creatures which share a great number of similarities and share a common name with other groups. a group of animals or plants of the same kind....... back a group of organisms ( individuals ) that can interbreed and reproduce with each other. used to distinguish sexually reproducing organisms into groups. individuals from two different species cannot have offspring. they are said to be reproductively isolated. the biologist ernst mayr formulated this definition of a species advancing our understanding of the mechanism of evolution of higher organisms. for microbes, the species definition does not properly apply, because they do not reproduce sexually, but have an efficient mechanism to exchange genetic material even between evolutionarily distant forms. this exchange of genes is known as horizontal gene transfer. unlike sexual reproduction, it usually involves only a


definition does not properly apply, because they do not reproduce sexually, but have an efficient mechanism to exchange genetic material even between evolutionarily distant forms. this exchange of genes is known as horizontal gene transfer. unlike sexual reproduction, it usually involves only a fraction of an organisms genome that is being transferred and is a mechanisms of increasing genetic variability among microorganisms that does not depend on cellular reproduction ( cell division ). the scientific name of a plant ; the genus name and the specific epithet together ; also equal to the latin name or binomial a reproductively isolated aggregate of interbreeding organisms. in chemistry, a distinct kind of molecule, ion, or other structure. groups of actually ( or potentially ) interbreeding natural populations that are reproductively isolated from other such groups. reproductive isolation implies that interbreeding between individuals of two species normally is prevented by intrinsic factors. in biological systematics, group of organisms of common ancestry that are able to reproduce only among themselves and that are usually geographically distinct. see nt chemical species. group of living things that share many common traits. each species is different from every other species in one or more ways. term used to describe the group of like individuals. classically species were defined as organisms that share certain characteristics. kind or sort a group of animals or plants that have one or more characteristics in common.............. back a certain type of plant or animal the division of animal classification below genus. a group of animals having common attributes, designated by a common name, that has the same structure, and that can breed together. a group of organisms that are very much alike and reproduce in their natural environment. we belong to the human species. a cohesive historical lineage of ancestral - descendant populations of organisms that maintains its identity from other such lineages. a species comes into being at a branching event ( when one lineage becomes one or more lineages ), and ceases to exist either at a branching event ( when it gives rise to new species ) or when the lineage is terminated through extinction. a group of animals or plants, whose members breed naturally only with each other. a single kind of organism ; white - tail and mule are different species of deer more information for scientifically naming a plant. the species name follows the genus. caesalpinia ( genus ) pulcherrima ( species ). red bird - of - paradise ( common name ). level of taxonomy below genus. the second part of a bird ' s scientific name


the species name follows the genus. caesalpinia ( genus ) pulcherrima ( species ). red bird - of - paradise ( common name ). level of taxonomy below genus. the second part of a bird ' s scientific name is the species name. the species name is never capitalized. a group of similar individuals that can breed among themselves. a biological category used to classify organisms. a group of plants or animals that are uniquely distinguished from others, sharing various characteristics, and usually that are able to reproduce. species are often broken down into additional subcategories, such as sub - species or varieties. one of the major classifying categories of taxonomy, representing divisions of a genus, and sometimes further classified into subspecies. used when naming plants. designates a specific species of the ' genus ' and is best described as the plant worlds equivalent to our christian names ( or first names ). will follow the genus name and is usually in latin. note : once a plants full name is used, i. e. hedera helix, future listings will abbreviate the genus name and follow it with the species name. an example would be, h. helix, as the next plant in a listing. group of organisms which interbreed and are reproductively isolated from all other such groups. the basic unit of taxonomic classification, designating a group of closely related individuals that are capable of interbreeding. a group of organisms defined by their ability to interbreed with only each other. a segment of a population - level lineage that is evolving separately from other such lineage segments as indicated by one or more lines of evidence ( e. g., distinguishability, reproductive isolation, monophyly, etc. ). the most specific taxonomic classification ; an interbreeding population of individual organisms ; often abbreviated as ' sp. ' in reference to a single species or ' spp. ' when referencing several species the fundamental biological classification consisting of very similar plants or animals. genetically distinct population ( s ) that interbreed but are reproductively isolated from other such groups. a group of individuals that share features and are able to interbreed under natural conditions to yield fertile offspring. a group of populations capable of successfully interbreeding and reproductively isolated from other such populations ( the white - tailed deer is a common species of mammal found in the pinelands. ) a biological type ; on msdss, species refers to the test animals - - usually rats, mice, or rabbits - - which were used to obtain


( the white - tailed deer is a common species of mammal found in the pinelands. ) a biological type ; on msdss, species refers to the test animals - - usually rats, mice, or rabbits - - which were used to obtain the toxicity test data reported. a class of individuals having common attributes and designated by a common name ; a category of biological classification ranking immediately below the genus or subgenus ; comprising related organisms or populations potentially capable of interbreeding. 1. freely interbreeding population of organisms. the organisms in a species usually share a large number of characters. their offspring are fertile. ( some species can interbreed, but their offspring are infertile. ) 2. generally the lowest level in a taxonomy. a category of animals or plants below a genus. sometimes breed is specified below it, such as for cultivated plants. a group of organisms that are closely related a taxonomic category of individuals or populations capable of breeding among themselves, but not usually with other individual or populations a group of organisms with many common characteristics ; a collection of closely related strains sufficiently different from all other strains to be recognized as a distinct unit. animals, plants or micro - organisms that are so similar that they are able to have offspring. group of similar individuals having a number of correlated characteristics and sharing a common gene pool. the species is the basic unit of taxonomy on which the binomial system has been established. the scientific name of a plant or animal gives the genus first and then the species as in abies ( genus ) grandis ( species ). species is both the singular and plural form of the word. groups or individuals of closely connected plants within a genus. a natural population that can breed and produce fertile offspring. a distinct population that tends, in nature, not to mix reproductively with other populations. a group of organisms that can breed or produce offspring taxonomic designation for the unique name of a living organism. a group of individuals of common ancestry that closely resemble each other structurally and physiologically and that can interbreed, producing fertile offspring. part of the plant classification system. this is used to describe closely related plants. see also genus and family. a class of individuals having some common characteristics or qualities. the taxonomic unit ( the most specific taxonomic category ). it designates individuals with similar morphologic structures, who can reproduce with each other. a particular kind of plant or animal ; all members of a species share certain characteristics and are known by a specific name. a subspecies is a division of a species. it


individuals with similar morphologic structures, who can reproduce with each other. a particular kind of plant or animal ; all members of a species share certain characteristics and are known by a specific name. a subspecies is a division of a species. it is hard to define a species absolutely because the process of one species becoming two or changing into another species is so slow that there is no point at which one can say ' now! it ' s a different species from yesterday! '. the most simple definition is a group of organisms that can breed together to produce fertile offspring. species are the smallest unit of biological taxonomy, and are grouped together with similar species to form a genus. the name given to a single kind of organism. species can be divided into sub - species. a group of interbreeding organisms that can produce offspring with the capacity for viable reproduction. the smallest unit in biological classification. members of the same species are able to breed among themselves successfully. similar species are grouped within one genus. a group of individuals with certain common characteristics a group of individuals or populations that are similar in structure and physiology and are capable of interbreeding and producing fertile offspring. separate species typically are different in structure and / or physiology from each other and normally do not interbreed. a species name is the second word of a scientific name and is not capitalized. living things such as plants and animals. a genetic subdivision whose numbers are capable of mating and producing fertile progeny group of animals or plants subordinate in classification to genus that can interbreed and differ only in minor details. a population of individuals that are more or less alike and that are able to breed and produce fertile offspring. a category of biological grouping just below the genus or subgenus level. a group of biologically distinct organisms that are self - perpetuating a naturally occurring population or group of potentially interbreeding populations that is reproductively isolated ( i. e., cannot exchange genetic material ) from such other groups. this definition does not apply to asexually reproducing forms such as many types of monera or protista, etc. individuals of the same type which are able to interbreed to produce fertile offspring under natural conditions contributing to a common gene pool. living things that are grouped by their common attributes and can reproduce only among themselves. human beings are one species ; dogs are another. distinct kinds of individual plants or animals that have common traits and share a common name. population of organisms that can interbreed and produce offspring that can also reproduce with one


can reproduce only among themselves. human beings are one species ; dogs are another. distinct kinds of individual plants or animals that have common traits and share a common name. population of organisms that can interbreed and produce offspring that can also reproduce with one another. a closed gene pool. taxon for biological species based on binomial nomenclature, italicized and using genus and trivial name ; e. g., triceratops horridus, tyrannosaurus rex. a group of related plants or animals that can interbreed to produce offspring. ( spe · cies ). a population of interbreeding organisms that are capable of, and do under natural conditions, reproduce fertile offspring. a group of organisms that are similar and can interbreed. a group of animals that can have young who can also have young ( this word should really be in a science glossary ) a group of animals and plants that have many things in common, and are different in at least one other way from all others. a group of similar creatures that produce viable young when breeding. a population or group of populations that are in reproductive contact but are reproductively isolated from all other populations. a group of interbreeding plants or animals. subspecies and races are subgroups of individuals of the same species in the process ( called speciation ) of becoming a separate species. a distinct kind of wood. plants or animals that are the same as each other and breed only with one another. a population of plants whose members are potentially able to breed with each other and which is reproductively isolated from other populations. living things of the same kind that are potentially able to breed together and produce fertile offspring ( i. e., offspring that themselves can reproduce ). usually, different species cannot interbreed but this rule is not absolute ( for example, a horse and donkey can interbreed to produce a mule, although this animal cannot reproduce, see hybrid ). even within one species, interbreeding may not always occur because of natural barriers. among some plants and many micro - organisms, the concept of a species does not always work. in these groups, species that appear different may be able to successfully create offspring under certain circumstances. a group of similar organisms that have a shared origin and the ability to breed freely with one another. the basic category in the linnaean sequence. a species may best be defined as a group of inter - breeding individuals with so many features in common that they form a distinct, and generally recognisable, group


breed freely with one another. the basic category in the linnaean sequence. a species may best be defined as a group of inter - breeding individuals with so many features in common that they form a distinct, and generally recognisable, group. in practice, the interbreeding criterion cannot always be used, for example with fossils, so species can often only be defined subjectively. one or more species are included in a genus. more on the species concept a group of individuals taxonomically ordered according to common attributes and designated by a common name. a single type of plant or animal, not a group like genus or family. each species has a two - word scientific name that includes the name of the genus it belongs to and then the name of the species. another way to think of this is the genus is the " generic " name and the species is the " specific " name. a specific kind of something ; " a species of molecule " ; " a species of villainy " a breeding population that can produce fertile offspring among its members, but not outside its group a classification of life forms that share enough genetic traits that they can interbreed to produce offspring that are still able to breed a collection of genetically similar individuals a collection of organisms that evolved according to darwin ' s five laws a collection of populations, all genetically related a constant succession of similar individuals that can reproduce together a diagnosable cluster of individuals within which there is a parental pattern of ancestry and descent, beyond which there is not, and which exhibits a pattern of phylogenetic ancestry and descent among units of like kind a distinct, qualitatively definite state of living matter a freely interbreeding population whose members do not interbreed with those of other populations a grouping of individuals that interbreed successfully a group of actually or potentially interbreeding natural populations reproductively isolated from other such populations a group of animals or plants all of which are similar enough in form to be considered as minor variations of the same organism a group of animals which can breed together, but who can ' t breed with others a group of animals which have a number of features in common and which are not shared by any other group of animals a group of animals with similar physical characteristics that can and do interbreed and share the same gene pool a group of freely interbreeding individuals that will not interbreed with other members of the same genus in its natural environment a group of individuals that can reproduce together a group of insects having many characteristics in common which differ from all other forms in one or


group of freely interbreeding individuals that will not interbreed with other members of the same genus in its natural environment a group of individuals that can reproduce together a group of insects having many characteristics in common which differ from all other forms in one or more ways a group of living organisms ( plants, animals, or microbes ) that breed under natural and to which many human cultures have become adapted a group of living organisms ( plants, animals, or microbes ) that breed under natural conditions and are reproductively isolated from other populations a group of morphologically similar organisms that can and do interbreed, thus sharing the same gene pool a group of morphologically similar organisms which can and do reproduce with one another a group of organisms - plant, animal, or microbe - of a single kind a group of organisms sharing a closely related common gene pool because of frequent interbreeding a group of organisms so similar to one another that they can interbreed a group of organisms that a ) have the same evolutionary ancestor a group of organisms that are so genetically similar that they can interbreed and produce fertile offspring a group of organisms that can interbreed and create viable offspring a group of organisms that can interbreed in nature to a group of organisms that can willingly and successfully interbreed, creating reproductively capable offspring of a similar type a group of organisms that have structural, functional, and developmental similarities and that are able to interbreed and produce fertile offspring a group of organisms that interbreed naturally among themselves but not with individuals from other groups a group of organisms that look alike and can breed among themselves and a genus is a broader division of classification a group of organisms that normally interbreed in nature to produce fertile offspring a group of organisms that recognize each other for the purpose of mating and fertilization a group of organisms whose members can interbreed in nature and produce viable, offspring, though this concept cannot apply to organisms or to fossils a group of organisms with a unique set of characteristics ( body shape and behavior, for example ) that distinguishes them from other organisms a group of plants or animals that are genetically similar and so are able to reproduce with each other a group of plants or animals that breed together but do not breed outside the group a group of plants or animals whose genes are so similar that they can breed together and produce fertile offspring a group of populations through which genes can flow and whose offspring have a fitness equal to the parents a group of population s whose individual members would, if given the opportunity, interbreed a group


so similar that they can breed together and produce fertile offspring a group of populations through which genes can flow and whose offspring have a fitness equal to the parents a group of population s whose individual members would, if given the opportunity, interbreed a group of populations whose individual members would, if given the opportunity, interbreed with individuals of other populations of that group a group of related individuals or populations which are potentially capable of interbreeding and producing fertile offspring a group of sexually - reproducing, interbreeding individuals that under normal conditions are unable to interbreed with another group a group of similar organisms that can mate to produce fertile, viable offspring a group or population of similar organisms that reproduce among themselves but do not naturally reproduce with any other kinds of organisms a life form that cannot breed successfully other than with its own kind a lineage ( an ancestor descendant sequence ) of populations or organisms that maintains its identity from other such lineages and which has its own evolutionary tendencies a more finely tuned group whose members share the same general characteristics an actually or potentially interbreeding population that does not interbreed with other such populations when there is opportunity to do so an arbitrary class or cluster of organisms given a name as a handle an array of populations which are actually or potentially interbreeding, and which are reproductively isolated from other such arrays under natural conditions ' an article from the business ( international ) category an assemblage of individuals agreeing with each other in all essential characters of vegetation and fructification, capable of reproducing perfect seed from which progeny can be reared an evolved or evolving, genetically distinctive, reproductively isolated, natural population an excellent diagnostic characteristic for s an important biological grouping of organisms whose members have similar structures, normally interbreed, and produce fertile offspring an intrabreeding population, which rarely breeds with a different breeding population an isolated group of individuals whose sum of characters tends to keep constant by natural inbreeding an organic form which, for periods of great and indefinite length as compared with the duration of human life, fluctuates only within narrow limits a particular kind of organism a pool of organisms that can exchange their genetic information a population of beings that can reproduce sexually and produce fertile offspring a population of individual organisms that can interbreed in nature, mating and producing fertile offspring in a natural setting a population of indiviuals who interbreed, as opposed to a population of organisms who merely share the same environment a population of organisms that can interbreed with eachother, not not


mating and producing fertile offspring in a natural setting a population of indiviuals who interbreed, as opposed to a population of organisms who merely share the same environment a population of organisms that can interbreed with eachother, not not other populations a population of organisms which are capable, under natural conditions, of interbreeding and producing viable offspring, and which are reproductively isolated from other similar groups a population that interbreeds and is reproductively isolated from other populations a set of individuals who can interbreed and have fertile progeny a set of populations capable of combining with each other but not with other similar sets of populations on the basis of affinity and co - direction in ecological speciation a single lineage of ancestral descendant populations of organisms which maintains its identity from other such lineages and which has its own evolutionary tendencies and historical fate a single organism, not a group a single type of organism a special group a specific name given to a plant or animal a subjective unit insofar as it is based on only a sample of the population and insofar as the point of separation where there is some overlap must be arbitrary a group of related living things that have characteristics in common a group of animals that mate together successfully ; a naming classification a unique group of animals, different from other groups. a class of individuals or objects grouped by virtue of their common attributes and assigned a common name. populations of organisms that may interbreed and produce fertile offspring having similar structure, habits, and functions. a group of related animals or plants that differ only in minor attributes ; able to interbreed among themselves a group of individuals that are capable of breeding and producing fertile offspring under natural conditions. a basic taxonomic group consisting of individuals of common ancestry who strongly resemble each other physiologically and who interbreed, producing fertile offspring. the sub - genus classification of salmonids being sampled. a kind of organism ; organisms that are very similar to one another ; they usually reproduce only among themselves one of the lowest principal biological classification units, which recognizes distinct ( non - interbreeding ) groups of similar organisms. a particular group of plant or animal that can only reproduce with others of the same kind. usually, the smallest unit of classification ; includes individuals which can breed with each other, produce viable offspring, have the same chromosome number, and share a common gene pool. group of similar plants which can freely interbreed. a group of similar plants or animals which will interbreed a group of living things that is very closely related and can interbre


have the same chromosome number, and share a common gene pool. group of similar plants which can freely interbreed. a group of similar plants or animals which will interbreed a group of living things that is very closely related and can interbreed. a gem with distinctive characteristics that are well defined. a group of very similar plants that can freely interbreed and are signified by the second word of the botanical name. see genus. the smallest taxonomic unit defining a group of animals or plants that are unable to breed to produce fertile offspring. the smallest taxonomic unit defining a group of animals that are unable to breed to produce fertile offspring. ( see classification ) a certain kind of animals within a closely related group subordinate classification to a genus ; reproductively isolated organisms that have common characteristics, such as eastern white pine or white - tailed deer. generally regarded as a group or organisms that resemble each other to a greater degree than members of other groups and that form a reproductively isolated group that will not normally breed with members of another group. the lowest - ranking common taxonomic rank. these names are not capitalized. the lowest major level of classification. a group of organisms that form an interbreeding population that is reproductively isolated from other populations all the individuals in a population that can breed and produce fertile young. a group of organisms different from all others in that they do not interbreed with any others. a group of individuals or populations that are similar and are able to mate and have offspring. a group of plants ( or animals ) showing intergradation among its individuals and having in common one or more characteristics which definitely separate it from any other group ; a kind of plant distinct from other plants. a group of similiar animals, reproductively isolated from all other such groups and able to breed and produce viable offspring. a group of plants or animals that share common characteristics a classification ranking just below the genus and made up of closely related plants that possibly can cross with one another. organisms that can reproduce their own kind ( see also genus ) ( a distinct animal or plant group that shares similar characteristics and can produce offspring within its group. ) a population of organisms which are able to interbreed freely under natural conditions. ( singular or plural ) : a group of plants or animals whose members breed naturally only with each other and resemble each other more closely than they resemble members of any similar group. a class of individuals having common attributes and designated by a common name ; a logical division of a genus or more comprehensive class ( merriam - webster


breed naturally only with each other and resemble each other more closely than they resemble members of any similar group. a class of individuals having common attributes and designated by a common name ; a logical division of a genus or more comprehensive class ( merriam - webster 1996 ). most specific level of scientific classification ; below genus the basic unit of classification which usually refers to one or several groups of plants or other living organisms that interbreed and maintain their distinctive identity through successive generations a class of individual plants or animals having some common characteristics or qualities which makes them distinct from other classes of plants or animals. the basic category of biological classification, ranking below the genus ; a species consists of related organisms or populations potentially capable of interbreeding ; a species is designated by a two part name consisting of its genus and a specific epithet ; see also subspecies a group of organisms ( living things ) capable of reproducing to give fertile off - spring. momo organisms that can interbreed and produce fertile offspring. a group of individuals biologically capable of interbreeding and which have a common ancestor. organisms that are genetically related, similar physically, and can reproduce viable offspring. this is the most useful taxonomical name because every living creature is assigned a unique species name, which is composed of two parts. a class of plants or animals having common attributes and designated by a common name. theoretically, plants or animals of different species cannot interbreed. however, occasionally this does not hold true. espece familienbezeichnung, f especie a population or series of populations whose individuals have the potential to freely breed with one another and that is discontinuous in variation from other populations or series of populations ; a fundamental category of taxonomic classification, ranking a kind of plant that is distinct from other plants. a group of organisms that are biologically capable of breeding and producing fertile offspring. it is the lowest normal taxonomic unit in use. meagher, 1991 a population of morphologically similar organisms that can reproduce sexually among themselves but that cannot produce fertile offspring when mated with other organisms. a group of organisms that have similar characteristics and can interbreed to produce fertile offspring. this is the defining identification of a living organism. based upon taxonomy it is usually a latinised adjective or noun and is never capitalised and is usually italicised. species may only have varieties after it, although the specific name may also be double - barreled. the basic unit of biological classification. generally defined as an aggregation of individuals similar in appearance