bluuebunny/crossref_metadata_2025 huggingface dataset:
Anticipating synchronization of chaotic systems with time delay and parameter mismatch
Authors: Han Qi , Li Chuandong , Huang Junjian
Published: January 2009

This paper studies the effect of parameter mismatch on anticipating synchronization of chaotic systems with time delay in the framework of the master-slave configuration. The convergence criteria for the error dynamical system under study are established by means of model transformation incorporated with Lyapunov functional and linear matrix inequality. The error bound of anticipating synchronization is estimated by rigorous theoretical analysis. Its accuracy is confirmed by numerical simulation results.
Thermal expansion of select Mn+1AXn (M=earlytransitionmetal, A=Agroupelement, X=C or N) phases measured by high temperature x-ray diffraction and dilatometry
Authors: Scabarozi T. H. , Amini S. , Leaffer O. , Ganguly A. , Gupta S. , Tambussi W. , Clipper S. , Spanier J. E. , Barsoum M. W. , Hettinger J. D. , Lofland S. E.
Published: January 2009

Herein we report on a systematic investigation of the thermal expansion of select Mn+1AXn phases. The bulk dilatometric thermal expansion coefficient αdil was measured in the 25–1200 °C temperature range and the thermal expansion of more than 15 of these phases was studied by x-ray diffraction in the 25–800 °C temperature range. The coefficient of thermal expansion for the a axis αa ranged between (2.9±0.1)×10−6 °C−1 (Nb2AsC) and (12.9±0.1)×10−6 °C−1 (Cr2GeC) while the coefficient for the c axis (αc) ranged between (6.4±0.2)×10−6 °C−1 (Ta2AlC) and (17.6±0.2)×10−6 °C−1 (Cr2GeC). Weak anisotropy in the thermal expansion was seen in most phases, with the largest value of αc/αa belonging to Nb2AsC. The Grüneisen parameters along the a and c directions were calculated from ab initio values for the elastic compliances and were relatively isotropic. A good correlation was found between the thermal expansion anisotropy and the elastic constant c13 and we conclude that the anisotropy in thermal expansion is related to the bonding between the M−A elements.
The Central Bureau for Astronomical Telegrams
Authors: Gingerich Owen
Published: January 2009

WHEN A NEW STAR bursts forth in the sky or a comet appears unexpectedly over the horizon, astronomers all over the world hope for prompt notification lest possible observations be irretrievably lost. To provide the required world-wide communications, the Central Bureau for Astronomical Telegrams operates under the auspices of the International Astronomical Union from the Smithsonian Astrophysical Observatory in Cambridge, Mass.
A hundred years of entropy
Authors: Dutta Mahadev
Published: January 2009

PERHAPS THE PARADOX of entropy is that it has so long a history and yet so many remaining puzzles. We might say that the roots of its history go back even to primitive man. In his struggle for existence he used crude appliances and discovered fire. From closer intimacy with more and more developed machines sprang mechanics, and from fire came the theory of heat; the two were quite separate sciences.
Electroluminescence
Authors: Thomas David G.
Published: January 2009

SOLIDS CAN GENERATE visible light in several ways. A solid raised to sufficiently high temperature, for example, will emit light, a principle that is used in the tungsten incandescent lamp. But practical considerations limit the efficiency and reliability of such a lamp. In electroluminescence, however, electronic energy can be converted directly into light, and in principle, there is nothing to prevent this process from being very efficient in a simple rugged device operating at room temperature (figures 1–3). Needless to say, such a possibility has aroused much curiosity.
Phimsy
Authors: Ellis R. Hobart
Published: January 2009

Henry memorabilia; Physics in the newspapers; Who's in the classroom?; Feymerwocky.
Visit to Argonne—II: Solid-State, Atomic and Nuclear Physics
Authors: Lubkin Gloria B.
Published: January 2009

Besides its high-energy-physics research (PHYSICS TODAY, February, page 57) Argonne National Laboratory has strong programs in nuclear, atomic and solid-state physics, and it is building a high-flux research reactor. During a recent visit there we spoke to some of the people in charge of these programs
Phimsy
Authors: Ellis R. Hobart
Published: January 2009

A degree becomes a kelvin; Miscounted those fringes; Astronomer's stamp; Clarity, justice, confusion; What is c if not a speed?; Toward better retrieval; Don't; listen to my opinion; Keeping builders up to date.
The emergence of rheology
Authors: Markovitz Hershel
Published: January 2009

THE DEFINITION of the newly coined word “rheology” in the constitution of the Society of Rheology, when it was founded in 1929 under Eugene C. Bingham of Lafayette College, was “fundamental and practical knowledge concerning the deformation or flow of matter.” As Markus Reiner recalled telling Bingham at the time, this word would appear to have the same meaning as the term continuum mechanics. An operational definition obtained by an examination of what most rheologists actually do would more likely lead to the conclusion that, as accurately as any scientific discipline can be defined, “rheology—a branch of mechanics—is the study of those properties of materials which determine their response to mechanical force,” a statement that appears in a brochure recently issued by the Society of Rheology. This more restricted view, the one that I shall take in delineating the area covered in this historical review, removes from consideration the more complicated flow and deformation problems usually discussed in fluid mechanics, hydrodynamics and elasticity.
Twenty years
Authors: Lubkin Gloria B.
Published: January 2009

PHYSICS TODAY is 20 years old this month; our first issue was published in May 1948. In this birthday issue we review some of the things that have happened in 20 years of physics and 20 years Of PHYSICS TODAY.
Twenty years of physics: The nucleus
Authors: Bromley D. Allan
Published: January 2009

NUCLEAR PHYSICS emerged from the war years in the 1940's as a field rich in applications but pitifully weak in fundamental understanding. In the next two decades, building on the impetus and insight achieved in the crash program of the 1940's, major progress has been made both in understanding and in application. The rich canvas of nuclear phenomena has been sketched in, and exquisite detail has emerged in many areas. Many other areas remain blank and await exploration and exploitation; indeed it has been necessary, repeatedly, to extend the boundaries of the canvas itself. Nuclear physics remains in the frontiers of man's understanding of his universe. To a unique degree it has also forced significant changes in contemporary society and civilization.
Twenty years of physics: Solid state
Authors: Ziman John M.
Published: January 2009

THE LAST TWO DECADES may well have been the era of solid-state physics. Certainly it has growed and growed; absolutely, of course, like all science and all physics, but also relatively to other fields. I guess it now occupies almost 40% of the family bed, instead of about 15% at the end of World War II. With its leading American and British exponents at the head of the National Academy of Sciences and in the Cavendish Chair, even the disciples of Rutherford are being forced to acknowledge its existence!
Twenty years of Physics Today: Today
Authors: Koch H. William
Published: January 2009

Two PREVIOUS AIP directors—Henry A. Barton and Elmer Hutchisson—have reviewed the earlier years of PHYSICS TODAY in the preceding pages. As the fourth and present director, I find this commemorative issue an ideal opportunity to comment on the way I see the publication and its future.
Neutral Excitation Seen In Superfluid Helium
Authors: Lubkin Gloria B.
Published: January 2009

Two Berkeley experimenters report they have produced a new kind of energetic neutral excitation in superfluid helium that travels centimeters without scattering. Clifford M. Surko and Frederick Reif, writing in Phys. Rev. Letters 20, 582 (1968) speculate that they are seeing an excited helium atom. If their interpretation is correct, the experiment is an interesting combination of atomic and low-temperature physics.
High-voltage electron microscopy
Authors: Cosslett V. Ellis
Published: January 2009

A SECOND GENERATION of electron microscopes, using ten times the voltage of conventional instruments, is beginning to fulfill designers' hopes of allowing study of thicker specimens with less radiation damage. Voltages in the 1-megavolt range have reduced the effect of chromatic aberration so that, a fixed value of resolution, usable specimen thickness can be increased roughly in the same ratio as voltage until it reaches a limit set by image visibility. Apart from a scaling up of the whole instrument, the only major difference in design is the insertion of an accelerator between the electron gun and the microscope itself. High-voltage instruments are being used in metal studies by investigators who want a specimen thick enough to display bulk properties and, in biology, to probe living matter. A still larger machine is under construction in France.
Computers and nuclear physics
Authors: Birnbaum Joel , Sachs Martin W.
Published: January 2009

TRANSFORMING RAW DATA from a nuclear-physics experiment into physical parameters and then to a publication follows a fairly universal course. For the past 20 years computers have performed more and more transformations. The first applications were primarily to the last stage, that is, transformation of reduced data into physically meaningful terms. As input and output devices connected to computers become more sophisticated, computers are put to work on more and more additional tasks. Today it is possible to have a computer perform most of the routine tasks in an experiment, perhaps even including the editing of a text for publication.
Holography and integral photography
Authors: Collier Robert J.
Published: January 2009

RECENT REVIVAL of interest in things optical, at least for those of us who have had only a desultory brush with formal training in optics, has been stimulated in the main by the emergence of the laser. Aimed with helium–neon, argon cw lasers and ruby pulsed lasers, many former microwave or laser physicists and electrical engineers have turned to exploring and exploiting that art of lensless photography called “holography.” Applying concepts from other disciplines to their new field, optical neophytes have done much to reveal the manifold potential of holography. Unlettered in optical lore, they have also at times blundered into the often unrewarding task of reinventing processes whose properties and limitations have long been investigated. Nevertheless such unwitting archeology does, on occasion, exhume an old idea that may be significant to current efforts and technology. While working with laser-illumination methods for recording and reconstructing three-dimensional images without lenses, holographers have become aware of older 3D image-recording techniques requiring myriads of lenslets. Whether lensless or lenslet, each of these (autostereoscopic) methods allows observation of a 3D image without special viewing apparatus.
Michael Faraday and the art of lecturing
Authors: Seeger Raymond J.
Published: January 2009

Michael Faraday's contributions to our understanding of electrical and magnetic phenomena are generally well known. Less familiar to many people is the importance of lectures in Faraday's own self-education and his subsequent teaching of others. He possessed an exceptional capacity for research and communication, a quality still evident in The Royal Institution, of which he had been director. This capacity was evident to all, both young and old, in a manner that was strikingly unique. For in his lectures he expressed all of the emotional and intellectual attributes of the natural philosopher possessed of genius. Lectures, for Faraday, reflected an approach to life involving all aspects of the personality in intimate relation to phenomena.
Pulsars
Authors: Maran Stephen P. , Cameron A. G. W.
Published: January 2009

THE DISCOVERY OF PULSARS, or rapidly pulsating radio sources, was, like certain other historic events in astronomy, an accident. It is reminiscent of the unexpected detection of radio bursts from Jupiter by Bernard F. Burke and Kenneth L. Franklin, who were studying the Crab Nebula, and of the discovery of the cosmic fireball radiation by Arno A. Penzias and R. W. Wilson, who had intended to survey the galactic continuum at high latitudes.
Dialog on dualism
Authors: Landé Alfred , Born Max , Biem Walter
Published: January 2009

LANDE: Concerning “the historical origin of the dualistic interpretation” which I “have not realized:” I know of course of Einstein's light quanta in opposition to light waves. But I also know that there is a unitary quantum theory of radiation that has relegated the “photon” to the role of a quantum number attached to the periodic components of the continuous Maxwell field; thereby it has become unnecessary to attribute various ad hoc invented quantities—spin, interdependence of electric and magnetic properties of the photon—in order to save a particle picture dual to the wave picture of light. Light waves are real, matter waves are imaginary, in more than one sense.
Phimsy
Authors: Ellis R. Hobart , Mackay Alan
Published: January 2009

Good new use for bad old guns; How about decimal time?; Does anybody here know d'Abro?; Acoustics at Hastings; The Omphalosceptic.
The new organization of physics students
Authors: Cunningham Donald E. , Seagondollar L. Worth , Shugart Cecil G. , Strassenburg Arnold A. , White Marsh W.
Published: January 2009

“DON'T TRUST anyone over 30!” This slogan—so disheartening to the elderly but sincere teacher—indicates that youth has at last realized what older generations have long known: The hope of the future lies with young idealists who have not yet found it expedient to accommodate. Although it is important to encourage youthful enthusiasms that lead to social improvements, it is also essential that the energies of our students be channeled toward constructive activities that serve as preparation for useful and responsible roles in society.
Is This a Quark I See Before Me?
Authors: Lubkin Gloria B.
Published: January 2009

A group at the University of Sydney has found five tracks in high-energy cosmic-ray air showers whose “appearance was that expected for a quark of charge 2/3 e.” The group, headed by Charles B. A. McCusker, used an array of scintillation counters, which triggered four delayed-expansion cloud chambers when an extensive air shower arrived. Each chamber is expanded 100 millisec after the shower arrives, and the vapor trail is photographed 200 millisec later.
Serpukhov Data Suggest Asymptopia May Be Further Away Than Ever
Authors: Lubkin Gloria B.
Published: January 2009

With 70 GeV available at the Soviet Serpukhov accelerator, a new look into the asymptotic region is possible, and some observers are surprised at the glimpses reported at the Lund International Conference on Elementary Particles in July. Preliminary results suggest that the π−-p and K−-p total cross sections may be flattening out as energy increases; many theorists had predicted that these cross sections would go down as energies increased.
Ultracold Neutrons May Refine Electric-Dipole-Moment Value
Authors: Rothenberg Marian S.
Published: January 2009

A group from the Joint Institute for Nuclear Research at Dubna, F. L. Shapiro, V. I. Lushchikov, Yu. N. Pokotilovskii and A. V. Strelkov, has trapped very low energy (10−7 eV) neutrons that could be used for sensitive electric-dipole-moment experiments. Because these ultracold neutrons have low velocities, they are present for a relatively long time in an experiment chamber and are thus more susceptible to effects than are faster particles.
Plasmas
Authors: Grad Harold
Published: January 2009

THE TENOR OF OUR TIMES is receptive to a very young science that claims dominion over 99% of the matter in the universe, proposes to fuel a cross-country auto trip with the deuterium from one gallon of sea water, offers to replace the magic of catalysis in polymer chemistry with precise knob turning, promises to alleviate the pollution problem by instant vaporization of waste and garbage, ventures to propel space ships and essays a role in cosmology. Even though these specific future applications of plasma physics are not proven, the potentialities of plasma, the “fourth state” of matter, are difficult to overstate.
More about tachyons
Authors: Bilaniuk Olexa-Myron , Brown Stephen L. , DeWitt Bryce , Newcomb William A. , Sachs Mendel , Sudarshan E. C. George , Yoshikawa Shoichi
Published: January 2009

“Anything that is not forbidden is compulsory,” says Murray Gell-Mann's half-facetious totalitarian principle. What then about faster-than-light particles called “tachyons”? In their May article Olexa-Myron Bilaniuk and E. C. George Sudarshan argued that valid solutions of Albert Einstein's relativity equations describe such particles. Thus if Einstein's equations are accurate descriptions of the physical universe and if solutions not forbidden are compulsory, tachyons must exist.
Measuring It Better: A Visit to Bureau International des Poids et Mesures
Authors: Ellis R. Hobart
Published: January 2009

If you drive west from Paris toward Versailles, you can easily pass through the little town of Sèvres without knowing that in it is the International Bureau of Weights and Measures. Only when you turn through a narrow arched gateway and climb a few hundred yards through the woods to a small clearing in the Pare de St Cloud do you come to the little historic manor, Pavilion de Breteuil.
Glassy Semiconductors Show Switching and Memory Effects
Authors: Lubkin Gloria B.
Published: January 2009

Switching and memory behavior in glassy semiconductors has been reported by Stanford R. Ovshinsky (of Energy Conversion Devices, Inc., Troy, Michigan) in the 11 Nov. issue of Phys. Rev. Letters. The report made headlines in newspapers like The New York Times and The Wall Street Journal, which played up the potential commercial and military applications of Ovshinsky's report.
An operational interpretation of nonrelativistic quantum mechanics
Authors: Lamb Willis E.
Published: January 2009

WHAT IS QUANTUM MECHANICS? A remarkable feature of the 1968 conference of Nobel prize winners in physics at Lindau is that it was possible for me to ask such a question in the presence of two of the founders of quantum mechanics, Werner Heisenberg and P.A.M. Dirac, more than 30 years after the discovery, in a lecture attended by 400 students who had recently begun their study of the subject. Several answers to the question are possible. The only easy one is that quantum mechanics is a discipline that provides a wonderful set of rules for calculating physical properties of matter. For such simple systems as hydrogen and helium atoms the calculated energy levels agree with experiment to fantastic accuracy. In more complicated cases the computations are difficult and the accuracy is lower, but it is reasonable to believe, in principle at least, that the theory would be adequate if only the calculational problems could be overcome.
More Electron Rings: LRL Forms Them; Dubna Starts Extraction
Authors: Lubkin Gloria B.
Published: January 2009

A group from the Joint Institute for Nuclear Research, Dubna, is doing experiments to extract an electron ring from an electron-ring accelerator (smokatron), according to V. P. Sarantsev, who spoke at the March Particle Accelerator Conference in Washington. A 1.5-MeV electron beam is injected into the Dubna device and forms a doughnut, which is then compressed (PHYSICS TODAY, February 1968, page 51 and November 1968, page 61). Then hydrogen is injected, becomes ionized, and protons are trapped inside the ring.
Check of T Invariance in Electromagnetic Interaction
Authors: Lubkin Gloria B.
Published: January 2009

An apparent violation of time-reversal invariance in the electromagnetic interaction was reported at the New York American Physical Society meeting by David Bartlett, K. Goulianos, Carl Friedberg, Ira Hammerman and David Hutchinson of Princeton. The group compared angular distributions for n+p→γ+d with data from other sources on the inverse reaction γ+d→n+p to test reciprocity and hence check time-reversal invariance. In the experiment, neutron energies from 160 to 680 MeV were studied. At lower values of energy the angular distributions for both of the reactions matched. But at about 600 MeV, which corresponds to formation of the N* resonance, the curves did not match. Michael Longo (University of Michigan) and his collaborators in a similar experiment do not see the large effect reported by the Princeton experimenters. Although many particle physicists are excited about the observations, a typical attitude is, “Interesting if true.”
What happened to my paper?
Authors: Goudsmit Samuel A.
Published: January 2009

MANY AUTHORS worry about their paper only after it has been sent to an editor. They want to know what is being done to it, why publishing takes so long and whether their manuscript is gathering dust on an editor's desk. Why did the editor pick a hostile referee?
A Philistine asks for equal time
Authors: Dillon Sister Johnell
Published: January 2009

I FELT AN URGE to speak on the side of the Philistines, after reading Henry E. Duckworth's article “How to Live with the Philistines” (PHYSICS TODAY, September 1968, page 54). As an English teacher who roomed for two years with a physics teacher, I feel that I am a qualified spokesman.
Electron Cloud to Produce Highly Stripped Heavy Ions
Authors: Lubkin Gloria B.
Published: January 2009

Positive ions trapped in electron clouds are exciting interest among high-energy and low-energy physicists alike. While those interested in making high-energy protons (and perhaps heavy ions) are investigating the electronring accelerator or smokatron (PHYSICS TODAY, April, page 63) a group at Avco-Everett Research Laboratory is trying to use an electron cloud to make a source of highly stripped heavy ions for nuclear-physics experiments. Like the electron-ring accelerator, the Avco device uses external magnetic fields to control the motions of an electron cloud and then uses the electrostatic fields generated by these electrons to trap the ions and then strip them.
Phimsy
Authors: Ellis R. Hobart , Ahlborx Boye
Published: January 2009

For the man with no needs; Schlieren Effect; NBS metric wall chart; A page is a space is a page; Our German equivalent; Some attention from outside; Never trust anybody.
The postdoctoral research associate–instructor
Authors: Green Alex E. S.
Published: January 2009

OVER TWO YEARS AGO Richard Martin described some problems that have developed around the “superscholar” or postdoctorate on the US campus. He noted that the usefulness of the postdoctorate to society is being questioned, and many suspect that the appointment simply serves as a haven for professional students who contribute relatively little to society, or who in one way or another are delaying a useful and permanent adjustment to society.
AIP in 1968: Expansion and experimentation
Authors: Wiley John P.
Published: January 2009

FOR PHYSICS IN THE US 1968—a time of budget cuts and manpower problems—was the kind of watershed year historians choose to write books about. The American Institute of Physics, anticipating some developments and responding to others, expanded its services to meet new demands and experimented with new ways to fulfill its mission.
Sensors in the deep sea
Authors: Caldwell Douglas R. , Snodgrass Frank E. , Wimbush Mark H.
Published: January 2009

GREAT ADVANCES in deep-sea research have become possible with recent improvements in electronic instrumentation and development of large computers. Many of today's instrumental techniques in oceanography have resulted from developments associated with space exploration. Indeed similarities exist between outer-space and ocean-depth studies. Manned space vehicles have counterparts in deep submersible submarines with life-support systems that carry men to observe in the greatest depths of the sea, and instrumented satellites and space probes have counterparts in a new family of unmanned capsules that carry electronic systems with delicate sensors to measure and record the deep-sea environment. Electronic recording systems for instrumented capsules must be light and compact and have low power consumption and high reliability.
Information from deep-space tracking
Authors: Muller Paul M. , Sjogren William L.
Published: January 2009

THE REMARKABLE NAVIGATION feats of the US deep-space probes were accomplished because of the farsighted attitude assumed in the development of a radio tracking system at the Jet Propulsion Laboratory. It was probably not fully realized at the outset what an enormous amount of scientific information would eventually be extracted from the data.
Long-baseline interferometry
Authors: Burke Bernard F.
Published: January 2009

THE RAPID DEVELOPMENT of electronic technology has given man the ability to control electrical events in the time domain with extraordinary precision, just as the mechanical revolution of the last century improved, by orders of magnitude, our power to control linear dimensions of physical objects. Perhaps the only failure in the analogy is quantitative; linear dimensions are now controllable to parts in 108, whereas time sequences can be generated and measured to parts in 1014. The modern radio equivalent of Michelson's stellar interferometer is an interesting example of the revival of old mechanical principles in new electronic forms. The first motivation for building radio interferometers was the same as Michelson's: the angular resolution of sources of electromagnetic radiation. The principal difference lay in the limitation of the conventional techniques, for angular resolution of stars in the visible region of the electromagnetic spectrum is limited to a second of arc or so by the irregular refracting properties of the atmosphere, and the diffraction limit of a few minutes of arc for conventional radio telescopes is set by the size of the federal budget.
Lifetime of Compound Nucleus Is Measured by Crystal Blocking
Authors: Lubkin Gloria B.
Published: January 2009

In a time-of-flight experiment where the flight path is less than 0.01 nanometer and the time is 10−16 sec, the lifetime of a compound nucleus has been directly measured (probably for the first time). Combining solid-state physics with nuclear physics, Karl Ove Nielsen (Aarhus University, Denmark) and Walter M. Gibson (Bell Telephone Laboratories) determined the lifetime by measuring blocking patterns from single crystals. They reported their results at the Washington meeting of the American Physical Society.
Crystal Acts Like a Two-Dimensional Antiferromagnet
Authors: Lubkin Gloria B.
Published: January 2009

A single crystal of K2NiF4 acts like a two-dimensional antiferromagnet above a critical temperature Tn = 97.1 K, according to a recent experiment at Brookhaven. At the critical temperature the crystal undergoes an extremely sharp phase transition to long-range order in three dimensions. Then below that temperature the magnetization varies as (T−Tn)β where β = 0.15, again suggesting that the magnetic behavior is two dimensional.
The flavor group Δ(6n2)
Authors: Escobar J. A. , Luhn Christoph
Published: January 2009

Many non-Abelian finite subgroups of SU(3) have been used to explain the flavor structure of the standard model. In order to systematize and classify successful models, a detailed knowledge of their mathematical structure is necessary. In this paper, we shall therefore look closely at the series of finite non-Abelian groups known as Δ(6n2), its smallest members being S3 (n=1) and S4 (n=2). For arbitrary n, we determine the conjugacy classes, the irreducible representations, the Kronecker products, as well as the Clebsch–Gordan coefficients.
Dimension of kernel sections for damped nonautonomous wave equations with critical exponent
Authors: Ban Ailing , Zhou Shengfan , Han Xiaoying
Published: January 2009

In this paper, by using the boundedness of kernel sections in higher regular space, we obtain an uniform upper bound of Hausdorff dimension of the kernel sections for damped nonautonomous wave equation when the nonlinearity has a critically growing exponent, which improves the previous estimate of Hausdorff dimension of the kernel sections.
Phase behavior of polyelectrolyte solutions with salt
Authors: Lee Chi-Lun , Muthukumar Murugappan
Published: January 2009

We have computed the phase diagrams of solutions of flexible polyelectrolyte chains with added simple electrolytes. The calculations are based on our recent theory [M. Muthukumar, Macromolecules 35, 9142 (2002)], which accounts for conformational fluctuations of chains, charge density correlations arising from dissolved ions, hydrophobic interaction between polymer backbone and solvent, and translational entropy of all species in the system. The theory is at the mean field level and recovers the results of the restricted primitive model with the Debye–Hückel description for solutions of simple electrolytes without any polymer chains and those of the Flory–Huggins and scaling theories for uncharged polymers in the absence of charges or electrolytes. In constructing the phase diagrams, the chemical potential of each of the species is maintained to be the same in the coexisting phases and at the same time each phase being electrically neutral (Donnan equilibrium). Comparisons are made with a more constrained situation where the chemical potentials of the independent components are maintained to be the same in the coexisting phases. Our calculations predict several rich phenomena. Even for the salt-free solutions, two critical phenomena (corresponding to the Flory–Huggins-type and the restricted-primitive-model-type critical points) are predicted. The coupling between these two leads to two critical end points and triple points. In the presence of salt, the valency of electrolyte ions is found to influence drastically the phase diagrams. Specifically, the predicted liquid-liquid phase transitions in certain temperature ranges is reminiscent of the re-entrant-precipitation phenomenon observed experimentally for polyelectrolytes condensed with trivalent salts.
Effective field theory with a variable ultraviolet cutoff
Authors: Tetradis Nikolaos
Published: January 2009

The properties of strongly gravitating systems suggest that field theory overcounts the states of a system. Reducing the number of degrees of freedom, without abandoning the notion of effective field theory, may be achieved through a connection between the ultraviolet and infrared cutoffs. We provide an implementation of this idea within the Wilsonian approach to the renormalization group. We derive an exact flow equation that describes the evolution of the effective action. We discuss the implications for the existence of infrared fixed points and the running of couplings. We also give an alternative derivation in the context of the perturbative renormalization group.
Hyperspherical harmonics with arbitrary arguments
Authors: Meremianin A. V.
Published: January 2009

The derivation scheme for hyperspherical harmonics (HSH) with arbitrary arguments is proposed. It is demonstrated that HSH can be presented as the product of HSH corresponding to spaces with lower dimensionality multiplied by the orthogonal (Jacobi or Gegenbauer) polynomial. The relation of HSH to quantum few-body problems is discussed. The explicit expressions for orthonormal HSH in spaces with dimensions from two to six are given. The important particular cases of four- and six-dimensional spaces are analyzed in detail and explicit expressions for HSH are given for several choices of hyperangles. In the six-dimensional space, HSH representing the kinetic-energy operator corresponding to (i) the three-body problem in physical space and (ii) four-body planar problem are derived.
Canonical Hamiltonians for waves in inhomogeneous media
Authors: Gershgorin Boris , Lvov Yuri V. , Nazarenko Sergey
Published: January 2009

We obtain a canonical form of a quadratic Hamiltonian for linear waves in a weakly inhomogeneous medium. This is achieved by using the Wentzel–Kramers–Brillouin representation of wave packets. The canonical form of the Hamiltonian is obtained via the series of canonical Bogolyubov-type and near-identical transformations. Various examples of the application illustrating the main features of our approach are presented. The knowledge of the Hamiltonian structure for linear wave systems provides a basis for developing a theory of weakly nonlinear random waves in inhomogeneous media generalizing the theory of homogeneous wave turbulence.
Are the spectra of geometrical operators in loop quantum gravity really discrete?
Authors: Dittrich Bianca , Thiemann Thomas
Published: January 2009

One of the celebrated results of loop quantum gravity (LQG) is the discreteness of the spectrum of geometrical operators such as length, area, and volume operators. This is an indication that the Planck scale geometry in LQG is discontinuous rather than smooth. However, there is no rigorous proof thereof at present. Because the aforementioned operators are not gauge invariant, they do not commute with the quantum constraints. The relational formalism in the incarnation of Rovelli’s partial and complete observables provides a possible mechanism for turning a non-gauge-invariant operator into a gauge invariant one. In this paper we investigate whether the spectrum of such a physical, that is, gauge invariant, observable can be predicted from the spectrum of the corresponding gauge variant observables. We will not do this in full LQG but rather consider much simpler examples where field theoretical complications are absent. We find, even in those simpler cases, that kinematical discreteness of the spectrum does not necessarily survive at the gauge invariant level. Whether or not this happens depends crucially on how the gauge invariant completion is performed. This indicates that “fundamental discreteness at the Planck scale in LQG” is far from established. To prove it, one must provide the detailed construction of gauge invariant versions of geometrical operators.
Tellegen particles and magnetoelectric metamaterials
Authors: Kamenetskii E. O. , Sigalov M. , Shavit R.
Published: January 2009

In 1948 Tellegen [Philips Res. Rep. 3, 81 (1948)] suggested that an assembly of the lined up electric-magnetic dipole twins can construct a new type of an electromagnetic material. Until now, however, the problem of creation of the Tellegen medium is a subject of strong discussions. An elementary symmetry analysis makes questionable an idea of a simple combination of two (electric and magnetic) dipoles to realize local materials with the Tellegen particles as structural elements. In this paper we show that in search of sources with local junctions of the electrical and magnetic properties one cannot rely on the induced parameters of small electromagnetic scatterers. No near-field electromagnetic structures and no classical motion equations for point charges give a physical basis for realization of sources with a local junction of the electrical and magnetic properties. We advance a hypothesis that local magnetoelectric (ME) particles should be physical objects with eigenmode oscillation spectra and nonclassical symmetry breaking effects. Our studies convincingly prove this assumption. We show that a quasi-two-dimensional ferrite disk with magnetic-dipolar-mode oscillations is characterized by unique symmetry features with topological phases resulting in appearance of the ME properties. An entire ferrite disk can be characterized as a combined system with the eigenelectric and eigenmagnetic moments. The fields near such a particle are distinguished by special symmetry properties. The questions raised in this paper give new insights into a problem of realization of local ME composites.
Optimized equation of the state of the square-well fluid of variable range based on a fourth-order free-energy expansion
Authors: Espíndola-Heredia Rodolfo , del Río Fernando , Malijevsky Anatol
Published: January 2009

The free energy of square-well (SW) systems of hard-core diameter σ with ranges 1≤λ≤3 is expanded in a perturbation series. This interval covers most ranges of interest, from short-ranged SW fluids (λ≃1.2) used in modeling colloids to long ranges (λ≃3) where the van der Waals classic approximation holds. The first four terms are evaluated by means of extensive Monte Carlo simulations. The calculations are corrected for the thermodynamic limit and care is taken to evaluate and to control the various sources of error. The results for the first two terms in the series confirm well-known independent results but have an increased estimated accuracy and cover a wider set of well ranges. The results for the third- and fourth-order terms are novel. The free-energy expansion for systems with short and intermediate ranges, 1≤λ≤2, is seen to have properties similar to those of systems with longer ranges, 2≤λ≤3. An equation of state (EOS) is built to represent the free-energy data. The thermodynamics given by this EOS, confronted against independent computer simulations, is shown to predict accurately the internal energy, pressure, specific heat, and chemical potential of the SW fluids considered and for densities 0≤ρσ3≤0.9 including subcritical temperatures. This fourth-order theory is estimated to be accurate except for a small region at high density, ρσ3≈0.9, and low temperature where terms of still higher order might be needed.
An approach to assessing ultrasonic attenuation in molten magnesium alloys
Authors: Qian Ma , Ramirez A.
Published: January 2009

Few experimental data are available on ultrasonic attenuation in molten light alloys due to lack of means of characterization. An approach has been proposed and demonstrated to assessing ultrasonic attenuation in molten magnesium alloys based on the finding that the grain density in ultrasonicated magnesium alloy samples depends linearly on ultrasonic amplitude along the propagation direction. Hence, the attenuation of the ultrasonic amplitude with propagation distance can be effectively assessed according to the variations in the grain density with propagation distance. Metallographic analyses revealed that the dependence of grain density on propagation distance is best described exponentially with respect to different amplitudes. Consequently, the attenuation behavior of the ultrasonic amplitude with propagation distance can be described by the same exponential law. The characteristic ultrasonic attenuation coefficients in three benchmark molten magnesium alloys investigated were determined accordingly. The validation experiments confirmed the validity of the data produced. Ultrasonic attenuation shows dependence on alloy chemistry.
Electroconvection of liquid crystals: Tool for fabricating modulated polymer surfaces
Authors: Hoischen A. , Benning S. A. , Kitzerow H.-S.
Published: January 2009

Electrically induced dissipative structures in liquid crystals can be stored by the photocuring of reactive mesogens. Thus, spontaneous pattern formation can be used to fabricate phase gratings or polymer films with a periodic surface modulation from an initially uniform sample. Different patterns, both in the conductive and in the dielectric regimes, have been stored. Photopolymerization and subsequent investigation by atomic force microscopy provide a useful tool in analyzing dissipative structures, even if the lattice constants are smaller than 1 μm. This method indicates surface modulations with amplitudes of up to 12 nm and periodicities between 800 nm and several tens of micrometers. The influences of composition and curing conditions on the topography have been studied.
Miniature atomic magnetometer integrated with flux concentrators
Authors: Griffith W. Clark , Jimenez-Martinez Ricardo , Shah Vishal , Knappe Svenja , Kitching John
Published: January 2009

High permeability magnetic flux concentrators are used to enhance the sensitivity of an atomic magnetometer operating in the spin-exchange relaxation-free regime. The magnetometer uses a millimeter scale Rb87 vapor cell and either mu-metal or Mn–Zn ferrite flux concentrators. The measured sensitivity gives excellent agreement with calculations of thermal noise from the concentrator material. The mu-metal concentrators allow a sensitivity of 50fTHz−1∕2, limited by thermal current magnetic noise. The ferrite concentrators are limited by thermal magnetization noise at low frequencies, and reach a sensitivity of 10fTHz−1∕2 for frequencies above 125Hz.
Analysis of a strong mass-based flame stretch model for turbulent premixed combustion
Authors: Bastiaans R. J. M. , van Oijen J. A. , de Goey L. P. H.
Published: January 2009

In the present paper a theory describing effects of strong flame stretch on turbulent flame propagation [L. P. H. de Goey and J. H. M. ten Thije Boonkkamp, “A flamelet description of premixed laminar flames and the relation with flame stretch,” Combust. Flame 119, 253 (1999)] is extended to volume averaged quantities and validated with direct numerical simulation (DNS). The extended theory describes the fuel consumption rate in terms of subgrid scale contributions connected to propagation effects including strong flame stretch. In case there is no preferential diffusion present, it is predicted that the total consumption rate is not affected by local stretch at all. Then the total consumption is described by the unstretched mass burning rate multiplied with the flame surface density. DNSs of turbulent flame kernels have been carried out in order to support the results from the theory. The chemistry is described by application of the flamelet generated manifold technique. The strong stretch theory is shown to be valid up to realizations in the thin reaction zone regime by three independent methods. The local effects of stretch are described, evaluated, and interpreted. Locally the mass burning rate changes by fuel leakage tangential to the flame, but this has no integral effect. The method can be used for subgrid scale modeling of turbulent flame propagation.
A theoretical study of the effects of the charge state and size of gold clusters on the adsorption and dissociation of H2
Authors: Kang Guo-Jun , Chen Zhao-Xu , Li Zhe , He Xiang
Published: January 2009

The adsorption and dissociation of H2 on the neutral and charged gold clusters Aunm(m=0,±1;  n=1–6) is investigated using the density functional theory PW91 functional. H2 interacts very weakly with Aun−1, whereas the interaction with Aun+1 is relatively strong. The binding energies on neutral clusters are between those on the cationic and anionic systems. The binding energy decreases monotonically with the size increase of the cationic clusters while it goes up first and then goes down on the neutral systems with the maximum value of 0.78 eV at Au3. Au cations show no propensity for the dissociation barrier reduction and are thermodynamically unfavorable for the dissociation. For the first time we find that H2 dissociation involves valley-ridge inflection points on some clusters. Our results indicate that H2 dissociates facilely at low temperatures on both neutral and cationic Au4 and Au5. The phenomenon that H2 dissociation was not observed experimentally is not due to the higher dissociation barrier and weak binding of H2. We also show that the coordination number of the Au atom may not play a determining role in H2 dissociation.
Thermal links for the implementation of an optical refrigerator
Authors: Parker John , Mar David , Von der Porten Steven , Hankinson John , Byram Kevin , Lee Chris , Mayeda Michael K. , Haskell Richard , Yang Qimin , Greenfield Scott , Epstein Richard
Published: January 2009

Optical refrigeration has been demonstrated by several groups of researchers, but the cooling elements have not been thermally linked to realistic heat loads in ways that achieve the desired temperatures. The ideal thermal link will have minimal surface area, provide complete optical isolation for the load, and possess high thermal conductivity. We have designed thermal links that minimize the absorption of fluoresced photons by the heat load using multiple mirrors and geometric shapes including a hemisphere, a kinked waveguide, and a tapered waveguide. While total link performance is dependent on additional factors, we have observed net transmission of photons with the tapered link as low as 0.04%. Our optical tests have been performed with a surrogate source that operates at 625 nm and mimics the angular distribution of light emitted from the cooling element of the Los Alamos solid state optical refrigerator. We have confirmed the optical performance of our various link geometries with computer simulations using CODE V optical modeling software. In addition we have used the thermal modeling tool in COMSOL MULTIPHYSICS to investigate other heating factors that affect the thermal performance of the optical refrigerator. Assuming an ideal cooling element and a nonabsorptive dielectric trapping mirror, the three dominant heating factors are (1) absorption of fluoresced photons transmitted through the thermal link, (2) blackbody radiation from the surrounding environment, and (3) conductive heat transfer through mechanical supports. Modeling results show that a 1 cm3 load can be chilled to 107 K with a 100 W pump laser. We have used the simulated steady-state cooling temperatures of the heat load to compare link designs and system configurations.
Thickness-modulated optical dielectric constants and band alignments of HfOxNy gate dielectrics
Authors: He G. , Zhang L. D. , Liu M. , Zhang J. P. , Wang X. J. , Zhen C. M.
Published: January 2009

Thickness-modulated optical dielectric constants and band alignments of HfOxNy films grown by sputtering have been investigated by spectroscopic ellipsometry (SE) and x-ray photoelectron spectroscopy. Based on SE measurements, it has been noted that an increase in optical dielectric constant and band gap has been observed as a function of the film thickness. Analyses of thickness-dependent band alignment of the HfOxNy/Si system indicate that the valence band offset increases, but only slight change in the conduction band offset, resulting from the thickness-induced change in the structure. The suitable optical dielectric constants and band offsets relative to Si make sputtering-derived HfOxNy film a promising candidate for high-k gate dielectrics.
Petschek reconnection with a nonlocalized resistivity
Authors: Baty H. , Forbes T. G. , Priest E. R.
Published: January 2009

The impact of using a nonlocalized electrical resistivity having a spatially asymmetric profile is considered on two-dimensional steady-state magnetic reconnection. Starting from an initial Harris current sheet, time-dependent magnetohydrodynamic simulations are carried out over an entire spatial domain without any symmetry assumptions. It is shown that a stationary Petschek-like reconnection is obtained in the half-plane where a uniform resistivity is adopted. The latter configuration is maintained by a coexisting Petschek configuration that is formed in the second half-plane where the resistivity exhibits a classical exponentially decreasing variation. The structure of the central diffusion region is asymmetric, with a stagnation point flow which does not coincide with the X-point. These results suggest conditions under which a Petschek solution can indeed exist in the presence of a small uniform resistivity in the whole domain.