Phase transition in the bounded one-dimensional multitrap system

We have previously discussed the diffusion limited problem of the bounded one-dimensional multitrap system where no external fiel is included and pay special attention to the transmission of the diffusing particles through the system of imperfect traps. We discuss here the case in which an external field is included to each trap and find not only the transmission but also the energy associated with the diffusing particles in the presence and absence of such fields. From the energy we find the specific heat $C_h$ and show that for certain values of the parameters associated with the multitrap system it behaves in a manner which is suggestive of phase transition. Moreover, this phase transition is demonstrated not only through the conventional single peak at which the specific heat function is undifferentiable but also through the less frequent phenomenon of double peaks.Comment: 25 pages, 6 PS Figures, there have been introduced many changes including the remove of two figure

Dynamic Fluctuation Phenomena in Double Membrane Films

Dynamics of double membrane films is investigated in the long-wavelength limit including the overdamped squeezing mode. We demonstrate that thermal fluctuations essentially modify the character of the mode due to its nonlinear coupling to the transversal shear hydrodynamic mode. The corresponding Green function acquires as a function of the frequency a cut along the imaginary semi-axis. Fluctuations lead to increasing the attenuation of the squeezing mode it becomes larger than the `bare' value.Comment: 7 pages, Revte

Coiling Instabilities in Multilamellar Tubes

Myelin figures are densely packed stacks of coaxial cylindrical bilayers that are unstable to the formation of coils or double helices. These myelin figures appear to have no intrinsic chirality. We show that such cylindrical membrane stacks can develop an instability when they acquire a spontaneous curvature or when the equilibrium distance between membranes is decreased. This instability breaks the chiral symmetry of the stack and may result in coiling. A unilamellar cylindrical vesicle, on the other hand, will develop an axisymmetric instability, possibly related to the pearling instability.Comment: 6 pages, 2 figure

Flavor changing single top quark production channels at e^+e^- colliders in the effective Lagrangian description

We perform a global analysis of the sensitivity of LEP2 and e^+e^- colliders with a c.m. energy in the range 500 - 2000 GeV to new flavor-changing single top quark production in the effective Lagrangian approach. The processes considered are sensitive to new flavor-changing effective vertices such as Ztc, htc, four-Fermi tcee contact terms as well as a right-handed Wtb coupling. We show that e^+ e^- colliders are most sensitive to the physics responsible for the contact tcee vertices. For example, it is found that the recent data from the 189 GeV LEP2 run can be used to rule out any new flavor physics that can generate these four-Fermi operators up to energy scales of \Lambda > 0.7 - 1.4 TeV, depending on the type of the four-Fermi interaction. We also show that a corresponding limit of \Lambda > 1.3 - 2.5 and \Lambda > 17 - 27 TeV can be reached at the future 200 GeV LEP2 run and a 1000 GeV e^+e^- collider, respectively. We note that these limits are much stronger than the typical limits which can be placed on flavor diagonal four-Fermi couplings. Similar results hold for \mu^+\mu^- colliders and for tu(bar) associated production. Finally we briefly comment on the necessity of measuring all flavor-changing effective vertices as they can be produced by different types of heavy physics.Comment: 34 pages, plain latex, 7 figures embadded in the text using epsfig. Added new references and discussions regarding their relevance to the paper. Added more comments on the comparison between flavor-changing and flavor-diagonal contact terms and on the importance of measuring the Ztc verte

Albedo and Reflection Spectra of Extrasolar Giant Planets

We generate theoretical albedo and reflection spectra for a full range of extrasolar giant planet (EGP) models, from Jovian to 51-Pegasi class objects. Our albedo modeling utilizes the latest atomic and molecular cross sections, a Mie theory treatment of extinction by condensates, a variety of particle size distributions, and an extension of the Feautrier radiative transfer method which allows for a general treatment of the scattering phase function. We find that due to qualitative similarities in the compositions and spectra of objects within each of five broad effective temperature ranges, it is natural to establish five representative EGP albedo classes: a ``Jovian'' class (T$_{\rm eff} \lesssim 150$ K; Class I) with tropospheric ammonia clouds, a ``water cloud'' class (T$_{\rm eff} \sim 250$ K; Class II) primarily affected by condensed H$_2$O, a ``clear'' class (T$_{\rm eff} \gtrsim 350$ K; Class III) which lacks clouds, and two high-temperature classes: Class IV (900 K $\lesssim$ T$_{\rm{eff}}$ $\lesssim$ 1500 K) for which alkali metal absorption predominates, and Class V (T$_{\rm{eff}}$ $\gtrsim$ 1500 K and/or low surface gravity ($\lesssim$ 10$^3$ cm s$^{-2}$)) for which a high silicate layer shields a significant fraction of the incident radiation from alkali metal and molecular absorption. The resonance lines of sodium and potassium are expected to be salient features in the reflection spectra of Class III, IV, and V objects. We derive Bond albedos and effective temperatures for the full set of known EGPs and explore the possible effects of non-equilibrium condensed products of photolysis above or within principal cloud decks. As in Jupiter, such species can lower the UV/blue albedo substantially, even if present in relatively small mixing ratios.Comment: revised LaTeX manuscript accepted to Ap.J.; also available at http://jupiter.as.arizona.edu/~burrows/paper

On the joint residence time of N independent two-dimensional Brownian motions

We study the behavior of several joint residence times of N independent Brownian particles in a disc of radius $R$ in two dimensions. We consider: (i) the time T_N(t) spent by all N particles simultaneously in the disc within the time interval [0,t]; (ii) the time T_N^{(m)}(t) which at least m out of N particles spend together in the disc within the time interval [0,t]; and (iii) the time {\tilde T}_N^{(m)}(t) which exactly m out of N particles spend together in the disc within the time interval [0,t]. We obtain very simple exact expressions for the expectations of these three residence times in the limit t\to\infty.Comment: 8 page

The flavor changing top decay t-->c+sneutrino or sneutrino-->t+c(bar) in the MSSM without R-parity

Widths for the new flavor changing top quark decay t-->c+sneutrino or for the reversed sneutrino decay sneutrino-->t+c(bar) are calculated in the MSSM without R-parity conservation. For large \tan\beta, e.g., \tan\beta ~ m_t/m_b ~ 40, Br(t-->c+sneutrino) > 10^{-5} or Br(sneutrino-->t+c(bar)) > 10^{-6} in a relatively wide range of the supersymmetric parameter space as long as there is more than one non-zero R-parity violating coupling. In the best cases, with a typical squark mass around 100 GeV, we find that Br(t-->c+sneutrino) ~ 10^{-4} - 10^{-3} or Br(sneutrino-->t+c(bar)) ~ 10^{-5} - 10^{-4}. For \tan\beta ~ O(1) the corresponding branching ratios for both top or sneutrino decays are too small to be measured at the LHC. Therefore, the decays t-->c+sneutrino or sneutrino-->t+c(bar) appear to be sensitive to \tan\beta and may be detected at the LHC. The branching ratios of the corresponding decays to an up quark instead of a charm quark, e.g., t-->u+sneutrino or sneutrino-->t+u(bar), may also be similar.Comment: 23 pages, plain latex, 8 figures embadded in the text using epsfi

Mean-field phase diagram of disordered bosons in a lattice at non-zero temperature

Bosons in a periodic lattice with on-site disorder at low but non-zero temperature are considered within a mean-field theory. The criteria used for the definition of the superfluid, Mott insulator and Bose glass are analysed. Since the compressibility does never vanish at non-zero temperature, it can not be used as a general criterium. We show that the phases are unambiguously distinguished by the superfluid density and the density of states of the low-energy exitations. The phase diagram of the system is calculated. It is shown that even a tiny temperature leads to a significant shift of the boundary between the Bose glass and superfluid

The Moran model as a dynamical process on networks and its implications for neutral speciation

In genetics the Moran model describes the neutral evolution of a bi-allelic gene in a population of haploid individuals subjected to mutations. We show in this paper that this model can be mapped into an influence dynamical process on networks subjected to external influences. The panmictic case considered by Moran corresponds to fully connected networks and can be completely solved in terms of hypergeometric functions. Other types of networks correspond to structured populations, for which approximate solutions are also available. This new approach to the classic Moran model leads to a relation between regular networks based on spatial grids and the mechanism of isolation by distance. We discuss the consequences of this connection for topopatric speciation and the theory of neutral speciation and biodiversity. We show that the effect of mutations in structured populations, where individuals can mate only with neighbors, is greatly enhanced with respect to the panmictic case. If mating is further constrained by genetic proximity between individuals, a balance of opposing tendencies take place: increasing diversity promoted by enhanced effective mutations versus decreasing diversity promoted by similarity between mates. Stabilization occurs with speciation via pattern formation. We derive an explicit relation involving the parameters characterizing the population that indicates when speciation is possible.Comment: Improved analytical treatment of speciatio