Adaptive Ising Model and Bacterial Chemotactic Receptor Network

We present a so-called adaptive Ising model (AIM) to provide a unifying explanation for sensitivity and perfect adaptation in bacterial chemotactic signalling, based on coupling among receptor dimers. In an AIM, an external field, representing ligand binding, is randomly applied to a fraction of spins, representing the states of the receptor dimers, and there is a delayed negative feedback from the spin value on the local field. This model is solved in an adiabatic approach. If the feedback is slow and weak enough, as indeed in chemotactic signalling, the system evolves through quasi-equilibrium states and the ``magnetization'', representing the signal, always attenuates towards zero and is always sensitive to a subsequent stimulus.Comment: revtex, final version to appear in Europhysics Letter

Building validation tools for knowledge-based systems

The Expert Systems Validation Associate (EVA), a validation system under development at the Lockheed Artificial Intelligence Center for more than a year, provides a wide range of validation tools to check the correctness, consistency and completeness of a knowledge-based system. A declarative meta-language (higher-order language), is used to create a generic version of EVA to validate applications written in arbitrary expert system shells. The architecture and functionality of EVA are presented. The functionality includes Structure Check, Logic Check, Extended Structure Check (using semantic information), Extended Logic Check, Semantic Check, Omission Check, Rule Refinement, Control Check, Test Case Generation, Error Localization, and Behavior Verification

Different Ways of Reading, or Just Making the Right Noises?

What does reading look like? Can learning to read be reduced to the acquisition of a set of isolable skills, or proficiency in reading be equated with the independence of the solitary, silent reader of prose fiction? These conceptions of reading and reading development, which figure strongly in educational policy, may appear to be simple common sense. But both ethnographic data and evidence from literary texts suggest that such paradigms offer, at most, a partial and ahistorical picture of reading. An important dimension, neglected in the dominant paradigms, is the irreducibly social quality of reading practices

Transition from Baryon- to Meson-Dominated Freeze Out -- Early Decoupling around 30 A GeV?

The recently discovered sharp peak in the excitation function of the K+/pi+ ratio around 30 A GeV in relativistic heavy-ion collisions is discussed in the framework of the Statistical Model. In this model, the freeze-out of an ideal hadron gas changes from a situation where baryons dominate to one with mainly mesons. This transition occurs at a temperature T = 140 MeV and baryon chemical potential mu(B) = 410 MeV corresponding to an energy of sqrt(s) = 8.2 GeV. The calculated maximum in the K+/pi+ ratio is, however, much less pronounced than the one observed by the NA49 Collaboration. The smooth increase of the K-/pi- ratio with incident energy and the shape of the excitation functions of the Lambda/pi+, Xi-/pi+ and Omega/pi ratios all exhibiting maxima at different incident energies, is consistent with the presently available experimental data. The measured K+/pi+ ratio exceeds the calculated one just at the incident energy when the freeze-out condition is changing. We speculate that at this point freeze-out might occur in a modified way. We discuss a scenario of an early freeze-out which indeed increases K+/pi+ ratio while most other particle ratios remain essentially unchanged. Such an early freeze-out is supported by results from HBT studies.Comment: 8 pages, 5 figures, SQM2006 conference, Los Angeles, March 200

From soft harmonic phonons to fast relaxational dynamics in CH3_{3}NH3_{3}PbBr3_{3}

The lead-halide perovskites, including CH$_{3}$NH$_{3}$PbBr$_{3}$, are components in cost effective, highly efficient photovoltaics, where the interactions of the molecular cations with the inorganic framework are suggested to influence the electronic and ferroelectric properties. CH$_{3}$NH$_{3}$PbBr$_{3}$ undergoes a series of structural transitions associated with orientational order of the CH$_{3}$NH$_{3}$ (MA) molecular cation and tilting of the PbBr$_{3}$ host framework. We apply high-resolution neutron scattering to study the soft harmonic phonons associated with these transitions, and find a strong coupling between the PbBr$_{3}$ framework and the quasistatic CH$_{3}$NH$_{3}$ dynamics at low energy transfers. At higher energy transfers, we observe a PbBr$_{6}$ octahedra soft mode driving a transition at 150 K from bound molecular excitations at low temperatures to relatively fast relaxational excitations that extend up to $\sim$ 50-100 meV. We suggest that these temporally overdamped dynamics enables possible indirect band gap processes in these materials that are related to the enhanced photovoltaic properties.Comment: (main text - 5 pages, 4 figures; supplementary information - 3 pages, 3 figures

Neutron scattering study of a quasi-2D spin-1/2 dimer system Piperazinium Hexachlorodicuprate under hydrostatic pressure

We report inelastic neutron scattering study of a quasi-two-dimensional S=1/2 dimer system Piperazinium Hexachlorodicuprate under hydrostatic pressure. The spin gap {\Delta} becomes softened with the increase of the hydrostatic pressure up to P= 9.0 kbar. The observed threefold degenerate triplet excitation at P= 6.0 kbar is consistent with the theoretical prediction and the bandwidth of the dispersion relation is unaffected within the experimental uncertainty. At P= 9.0 kbar the spin gap is reduced to 0.55 meV from 1.0 meV at ambient pressure.Comment: 4 pages, 5 figure

Report on televiewer log and stress measurements in core hole USW G-2, Nevada Test Site, October-November, 1982

Hydraulic fracturing stress measurements and a borehole televiewer log were obtained in hole USW G-2 at Yucca Mountain, Nevada, to depths of 1200 m. Results indicate that at the depths tested, the minimum and maximum horizontal stresses are less than the vertical stress, corresponding to a normal faulting stress regime. Drilling-induced hydrofractures seen in the televiewer log imply a least horizontal principal stress direction of N 60° W to N 65° W. For reasonable values of the coefficient of friction, the magnitude of the least horizontal stress is close to the value at which slip would occur on preexisting faults of optimal orientation (strike N 25° E to N 30° E and dipping 60° to 67°). The prominent drilling-induced fractures seen in the televiewer log are believed to have been caused by excess downhole pressures applied during drilling the hole. Many throughgoing fractures are also seen in the televiewer log; most of these are high angle, stringking N 10° E to N 40° E. These fractures show a general decrease in angle of dip with depth. Stress-induced wellbore breakouts are seen at depths below 1050 m. The average N 60° W azimuth of these breakouts agrees very closely with the N 60° W to N 65° W direction of least horizontal principal stress inferred from the drilling-induced hydrofracs

Characterizing upward lightning with and without a terrestrial gamma-ray flash

We compare two observations of gamma-rays before, during, and after lightning flashes initiated by upward leaders from a tower during low-altitude winter thunderstorms on the western coast of Honshu, Japan. While the two leaders appear similar, one produced a terrestrial gamma-ray flash (TGF) so bright that it paralyzed the gamma-ray detectors while it was occurring, and could be observed only via the weaker flux of neutrons created in its wake, while the other produced no detectable TGF gamma-rays at all. The ratio between the indirectly derived gamma-ray fluence for the TGF and the 95% confidence gamma-ray upper limit for the gamma-ray quiet flash is a factor of $1\times10^7$. With the only two observations of this type providing such dramatically different results -- a TGF probably as bright as those seen from space and a powerful upper limit -- we recognize that weak, sub-luminous TGFs in this situation are probably not common, and we quantify this conclusion. While the gamma-ray quiet flash appeared to have a faster leader and more powerful initial continuous current pulse than the flash that produced a TGF, the TGF-producing flash occurred during a weak gamma-ray "glow", while the gamma-ray quiet flash did not, implying a higher electric field aloft when the TGF was produced. We suggest that the field in the high-field region approached by a leader may be more important for whether a TGF is produced than the characteristics of the leader itself.Comment: 21 pages, 6 figures, accepted for publication by the Journal of Geophysical Research - Atmosphere

Extension in the western Ross Sea region-links between Adare Basin and Victoria Land Basin

Spreading in the Adare Basin off north-western Ross Sea (43–26 Ma) and extension in the Victoria Land Basin (VLB, > 36 Ma) are used to constrain the pole of rotation for the Adare Basin, providing a rifting model for the region for the past 45 Ma. The offset from Northern Basin to VLB at about 74°S coincides with the linear Polar-3 magnetic anomaly, inferred to be caused by a major 48 - 34 Ma igneous intrusion. The style of extension apparently changed at about 34 Ma, with the end of intrusion at the Polar-3 anomaly, a change from highly asymmetric extension in Adare Basin, and the onset of major subsidence on the flanks of VLB. Ductile lower crustal and lithospheric flow is proposed as the cause of the inferred thick crust underlying southern Adare Basin, and a result of the constraining of extension to the adjacent contiguous Northern Basin

Midrapidity phi production in Au+Au collisions at sqrt[sNN]=130 GeV

We present the first measurement of midrapidity vector meson phi production in Au+Au collisions at RHIC (sqrt[sNN]=130 GeV) from the STAR detector. For the 11% highest multiplicity collisions, the slope parameter from an exponential fit to the transverse mass distribution is T=379±50(stat)±45(syst) MeV, the yield dN/dy=5.73±0.37(stat)±0.69(syst) per event, and the ratio N phi /Nh- is found to be 0.021±0.001(stat)±0.004(syst). The measured ratio N phi /Nh- and T for the phi meson at midrapidity do not change for the selected multiplicity bins.alle Autoren: C. Adler11, Z. Ahammed23, C. Allgower12, J. Amonett14, B. D. Anderson14, M. Anderson5, G. S. Averichev9, J. Balewski12, O. Barannikova9,23, L. S. Barnby14, J. Baudot13, S. Bekele20, V. V. Belaga9, R. Bellwied30, J. Berger11, H. Bichsel29, L. C. Bland12, C. O. Blyth3, B. E. Bonner24, A. Boucham26, A. Brandin18, R. V. Cadman1, H. Caines20, M. Calderón de la Barca Sánchez31, A. Cardenas23, J. Carroll15, J. Castillo26, M. Castro30, D. Cebra5, S. Chattopadhyay30, M. L. Chen2, Y. Chen6, S. P. Chernenko9, M. Cherney8, A. Chikanian31, B. Choi27, W. Christie2, J. P. Coffin13, T. M. Cormier30, J. G. Cramer29, H. J. Crawford4, M. DeMello24, W. S. Deng14, A. A. Derevschikov22, L. Didenko2, J. E. Draper5, V. B. Dunin9, J. C. Dunlop31, V. Eckardt16, L. G. Efimov9, V. Emelianov18, J. Engelage4, G. Eppley24, B. Erazmus26, P. Fachini25, V. Faine2, E. Finch31, Y. Fisyak2, D. Flierl11, K. J. Foley2, J. Fu15, N. Gagunashvili9, J. Gans31, L. Gaudichet26, M. Germain13, F. Geurts24, V. Ghazikhanian6, J. Grabski28, O. Grachov30, D. Greiner15, V. Grigoriev18, M. Guedon13, E. Gushin18, T. J. Hallman2, D. Hardtke15, J. W. Harris31, M. Heffner5, S. Heppelmann21, T. Herston23, B. Hippolyte13, A. Hirsch23, E. Hjort15, G. W. Hoffmann27, M. Horsley31, H. Z. Huang6, T. J. Humanic20, H. Hümmler16, G. Igo6, A. Ishihara27, Yu. I. Ivanshin10, P. Jacobs15, W. W. Jacobs12, M. Janik28, I. Johnson15, P. G. Jones3, E. Judd4, M. Kaneta15, M. Kaplan7, D. Keane14, A. Kisiel28, J. Klay5, S. R. Klein15, A. Klyachko12, A. S. Konstantinov22, L. Kotchenda18, A. D. Kovalenko9, M. Kramer19, P. Kravtsov18, K. Krueger1, C. Kuhn13, A. I. Kulikov9, G. J. Kunde31, C. L. Kunz7, R. Kh. Kutuev10, A. A. Kuznetsov9, L. Lakehal-Ayat26, J. Lamas-Valverde24, M. A. C. Lamont3, J. M. Landgraf2, S. Lange11, C. P. Lansdell27, B. Lasiuk31, F. Laue2, A. Lebedev2, T. LeCompte1, R. Lednický9, V. M. Leontiev22, M. J. LeVine2, Q. Li30, Q. Li15, S. J. Lindenbaum19, M. A. Lisa20, T. Ljubicic2, W. J. Llope24, G. LoCurto16, H. Long6, R. S. Longacre2, M. Lopez-Noriega20, W. A. Love2, D. Lynn2, R. Majka31, S. Margetis14, L. Martin26, J. Marx15, H. S. Matis15, Yu. A. Matulenko22, T. S. McShane8, F. Meissner15, Yu. Melnick22, A. Meschanin22, M. Messer2, M. L. Miller31, Z. Milosevich7, N. G. Minaev22, J. Mitchell24, V. A. Moiseenko10, D. Moltz15, C. F. Moore27, V. Morozov15, M. M. de Moura30, M. G. Munhoz25, G. S. Mutchler24, J. M. Nelson3, P. Nevski2, V. A. Nikitin10, L. V. Nogach22, B. Norman14, S. B. Nurushev22, G. Odyniec15, A. Ogawa21, V. Okorokov18, M. Oldenburg16, D. Olson15, G. Paic20, S. U. Pandey30, Y. Panebratsev9, S. Y. Panitkin2, A. I. Pavlinov30, T. Pawlak28, V. Perevoztchikov2, W. Peryt28, V. A. Petrov10, E. Platner24, J. Pluta28, N. Porile23, J. Porter2, A. M. Poskanzer15, E. Potrebenikova9, D. Prindle29, C. Pruneau30, S. Radomski28, G. Rai15, O. Ravel26, R. L. Ray27, S. V. Razin9,12, D. Reichhold8, J. G. Reid29, F. Retiere15, A. Ridiger18, H. G. Ritter15, J. B. Roberts24, O. V. Rogachevski9, J. L. Romero5, C. Roy26, D. Russ7, V. Rykov30, I. Sakrejda15, J. Sandweiss31, A. C. Saulys2, I. Savin10, J. Schambach27, R. P. Scharenberg23, N. Schmitz16, L. S. Schroeder15, A. Schüttauf16, K. Schweda15, J. Seger8, D. Seliverstov18, P. Seyboth16, E. Shahaliev9, K. E. Shestermanov22, S. S. Shimanskii9, V. S. Shvetcov10, G. Skoro9, N. Smirnov31, R. Snellings15, J. Sowinski12, H. M. Spinka1, B. Srivastava23, E. J. Stephenson12, R. Stock11, A. Stolpovsky30, M. Strikhanov18, B. Stringfellow23, C. Struck11, A. A. P. Suaide30, E. Sugarbaker20, C. Suire13, M. Sumbera9, T. J. M. Symons15, A. Szanto de Toledo25, P. Szarwas28, J. Takahashi25, A. H. Tang14, J. H. Thomas15, V. Tikhomirov18, T. A. Trainor29, S. Trentalange6, M. Tokarev9, M. B. Tonjes17, V. Trofimov18, O. Tsai6, K. Turner2, T. Ullrich2, D. G. Underwood1, G. Van Buren2, A. M. VanderMolen17, A. Vanyashin15, I. M. Vasilevski10, A. N. Vasiliev22, S. E. Vigdor12, S. A. Voloshin30, F. Wang23, H. Ward27, J. W. Watson14, R. Wells20, T. Wenaus2, G. D. Westfall17, C. Whitten, Jr.6, H. Wieman15, R. Willson20, S. W. Wissink12, R. Witt14, N. Xu15, Z. Xu31, A. E. Yakutin22, E. Yamamoto6, J. Yang6, P. Yepes24, A. Yokosawa1, V. I. Yurevich9, Y. V. Zanevski9, I. Zborovský9, H. Zhang31, W. M. Zhang14, R. Zoulkarneev10, and A. N. Zubarev