Is room-temperature superconductivity with phonons possible?

By recognizing the vital importance of two-hole Cooper pairs (CPs) in addition to the usual two-electron ones in a strongly-interacting many-electron system, the concept of CPs was re-examined with striking conclusions. Based on this, Bose-Einstein condensation (BEC) theory has been generalized to include not boson-boson interactions (also neglected in BCS theory) but rather boson-fermion (BF)interaction vertices reminiscent of the Frohlich electron-phonon interaction in metals. Unlike BCS theory, the GBEC model is not a mean-field theory restricted to weak-coupling as it can be diagonalized exactly. In weak coupling it reproduces the BCS condensation energy. Each kind of CP is responsible for only half the condensation energy. The GBEC theory reduces to all the old known statistical theories as special cases including the so-called "BCS-Bose crossover" picture which in turn generalizes BCS theory by not assuming that the electron chemical potential equals the Fermi energy. Indeed, a BCS condensate is precisely the weak-coupling limit of a GBE condensate with equal numbers of both types of CPs. With feasible Cooper/BCS model interelectonic interaction parameter values, and even without BF interactions, the GBEC theory yields transition temperatures [including room-temperature superconductivity (RTSC)] substantially higher than the BCS ceiling of around 45K, without relying on non-phonon dynamics involving excitons, plasmons, magnons or otherwise purely-electronic mechanisms.Comment: 14 pages, 2 figures, Mini-course delivered at "X Training Course in the Physics of Correlated-Electron Systems and High Tc Superconductors" Salerno, Italy, 3-14 October, 200

Anomalous behavior of ideal Fermi gas below two dimensions

Normal behavior of the thermodynamic properties of a Fermi gas in $d>2$ dimensions, integer or not, means monotonically increasing or decreasing of its specific heat, chemical potential or isothermal sound velocity, all as functions of temperature. However, for $0<d<2$ dimensions these properties develop a ``hump'' (or ``trough'') which increases (or deepens) as $d\to 0$. Though not the phase transition signaled by the sharp features (``cusp'' or ``jump'') in those properties for the ideal Bose gas in $d>2$ (known as the Bose-Einstein condensation), it is nevertheless an intriguing structural anomaly which we exhibit in detail.Comment: 14 pages including 3 figure

Testing Bayes Rule and the Representativeness Heuristic: Some Experimental Evidence

The psychological literature has identified a number of heuristics which individuals may use in making judgments or choices under uncertainty. Mathematically equivalent problems may be treated differently depending upon details of the decision setting (Gigerenzer et al. (1988), Hinz et al. (1988), Birnbaum and Mellers (1983), Ginossar and Trope (1987)) or upon how the decisions are framed (Tversky and Kahneman (1986)). The results presented in this paper are consistent with those findings and are unsettling. In equivalent problems subjects appear to adopt different strategies in response to observing different data. All problems were inference problems about populations represented by bingo cages and all randomization was operational and observed by the subjects. Thus one cannot explain the change of decision strategy by appeal to changing reference points nor should difference between surface and deep structure of problems apply (Wagenaar et al. (1988)). A striking observation from the experiments is the result of employing financial incentives. Some experiments included financial incentives for accuracy and some did not. In the latter experiments the number of nonsense or incoherent responses increased by a factor of three. The majority of subjects in both treatments behaved reasonably, but of those lacking financial incentives a larger proportion gave obviously absurd responses. This suggests that data from decision experiments in which no financial incentives were should be treated as possibly contaminated and statistical methods robust against outliers employed

A Note on Distributed Lags, Prediction, and Signal Extraction

[No abstract

Financial Incentive Effects and Individual Decision-making

Though much of the literature of experimental psychology covers topics that seem relevant to economics, the literature is generally ignored by economists. Possibly the reason for this is that psychologists seldom use financial incentives to motivate subjects' choices. This paper provides an example of an individual decision-making experiment in which the presence or absence of financial incentives affects the subjects' behavior. The observed effects are not marginal but often involve qualitatively different types of responses

Origin of nonlinear contribution to the shift of the critical temperature in atomic Bose-Einstein condensates

We discuss a possible origin of the experimentally observed nonlinear contribution to the shift $\Delta T_{c}=T_c-T_{c}^{0}$ of the critical temperature $T_{c}$ in an atomic Bose-Einstein condensate (BEC) with respect to the critical temperature $T_{c}^{0}$ of an ideal gas. We found that accounting for a nonlinear (quadratic) Zeeman effect (with applied magnetic field closely matching a Feshbach resonance field $B_0$) in the mean-field approximation results in a rather significant renormalization of the field-free nonlinear contribution $b_{2}$, namely $\Delta T_{c}/T_{c}^{0}\simeq b_{2}^{\ast }(a/\lambda _{T})^{2}$ (where $a$ is the s-wave scattering length, $\lambda _{T}$ is the thermal wavelength at $T_{c}^{0}$) with $b_{2}^{\ast }=\gamma ^{2}b_{2}$ and $\gamma =\gamma (B_0)$. In particular, we predict $b_{2}^{\ast }\simeq 42.3$ for the $B_{0}\simeq 403G$ resonance observed in the $\ ^{39}K$ BEC.Comment: Accepted for publication in JETP Letter

Research and Development Expenditures as a Competitive Strategy

Making a better mousetrap has been one of the standard methods of achieving competitive advantages in American industries. Of course, making an equally good mousetrap with lower costs can be just as effective. To the extent that businesses compete with each other with product and process improvements, then one would expect investment in these activities (research and development [R&D]) to be a primary competitive tool. It is natural to ask which types of firms tend to engage heavily in R&D. A clearly related question one might ask is which market structures are conducive to R&D activity and which are not. In addition, it is important to remember that market structure itself may be affected by firms' R&D activities--raising the question of R&D's impact on market structure (see the related paper by Preston in this volume). The most obvious situation in which market structure is affected by R&D activity is, of course, that of a monopoly position achieved and maintained by patents. This latter question; that is, essentially asking if market structure is really exogenous, is often not directly addressed in the literature. The purpose of this paper is to survey one portion of the so-called market structure literature, viz., the empirical literature dealing with the relation between market structure and the level of research and development activity. Weiss (1969) has surveyed the empirical literature in the entire field of industrial organization, and Kamien and Schwartz (1975) more recently surveyed the literature concerning innovative activity in general. In order to allow for an intensive examination of one body of literature, the scope of this paper has been kept narrow. Readers interested in other issues, for example, the rate of adoption or imitation and the diffusion of technological information, are referred to these other studies