Electrodynamics of superconductors

An alternate set of equations to describe the electrodynamics of superconductors at a macroscopic level is proposed. These equations resemble equations originally proposed by the London brothers but later discarded by them. Unlike the conventional London equations the alternate equations are relativistically covariant, and they can be understood as arising from the 'rigidity' of the superfluid wave function in a relativistically covariant microscopic theory. They predict that an internal 'spontaneous' electric field exists in superconductors, and that externally applied electric fields, both longitudinal and transverse, are screened over a London penetration length, as magnetic fields are. The associated longitudinal dielectric function predicts a much steeper plasmon dispersion relation than the conventional theory, and a blue shift of the minimum plasmon frequency for small samples. It is argued that the conventional London equations lead to difficulties that are removed in the present theory, and that the proposed equations do not contradict any known experimental facts. Experimental tests are discussed.Comment: Small changes following referee's and editor's comments; to be published in Phys.Rev.

Vortex Penetration into a Type II Superconductor due to a Mesoscopic External Current

Applying the London theory we study curved vortices produced by an external current near and parallel to the surface of a type II superconductor. By minimizing the energy functional we find the contour describing the hard core of the flux line, and predict the threshold current for entrance of the first vortex. We assume that the vortex entrance is allowed due to surface defects, despite the Bean-Livingston barrier. Compared to the usual situation with a homogeneous magnetic field, the main effect of the present geometry is that larger magnetic fields can be applied locally before vortices enter the superconducting sample. It is argued that this effect can be further enhanced in anisotropic superconductors.Comment: 9 pages, 14 figure

Obtaining the Full Unitarity Triangle from B -> pi K Decays

We present a method of obtaining the entire unitarity triangle from measurements of B -> pi K decay rates alone. Electroweak penguin amplitudes are included, and are related to tree operators. Discrete ambiguities are removed by comparing solutions with independent experimental data. The theoretical uncertainty in this method is rather small, in the range 5--10%.Comment: 4 pages, RevTeX, no figures. Clarifying remarks and references adde

Cloud information for FIRE from surface weather reports

Surface weather observations of clouds were analyzed to obtain a global cloud climatology (Warren et al, 1986; 1988). The form of the synoptic weather code limits the types of cloud information which are available from these reports. Comparison of surface weather reports with instrumental observations during the FIRE field experiments can help to clarify the operational definitions which were made in the climatology because of the nature of the synoptic code. The long-term climatology from surface weather observations is also useful background for planning the location and timing of intensive field experiments

A new pachyrhizodontid fish (Actinopterygii: Teleostei) from the Tarrant Formation (Cenomanian) of the Upper Cretaceous Eagle Ford Group of Texas, U.S.A.

SMU 76938 is a fossil skeleton of a large, nearly complete actinopterygian bony fish housed in Southern Methodist University in Dallas, Texas, USA. It was collected from the Upper Cretaceous Tarrant Formation (middle Cenomanian; ~96 Ma) of the Eagle Ford Group in Tarrant County, Texas, an area where it was near the western margin of the East Texas Embayment during the Late Cretaceous. Although parts of the skull and dorsal fin are damaged, SMU 76938 is relatively complete, especially in the preservation of the caudal fin with its soft tissue outline. The fish has a fusiform body and measures about 93, 109, and 119 cm in standard length, fork length, and total length, respectively, and about 17 cm in maximum body depth. Several features of SMU 76938 are reminiscent of Cretaceous crossognathiforms, yet many features, such as the villiform dentition, have yet to be seen in any taxa within the order. My phylogenetic analysis indicates that SMU 76938 is a pachyrhizodontid crossognathiform fish. The combination of villiform teeth and fused infraorbital 1 and 2 in SMU 76938 is unique, suggesting that the specimen belongs to a new genus and species within the family Pachyrhizodontidae. With a fusiform body, a large symmetrical caudal fin, and a mouth with numerous small conical teeth suited for grasping, the new taxon represented by SMU 76938 was most likely a fast swimming, open-ocean predator capable of high propulsion and quick bursts of speed, that likely pursued smaller, quick swimming animals, such as squid, crustaceans, and other fishes. Although the individual represented by SMU 76938 was about 14 years old at the time of its death, my vertebra-based theoretical growth model indicates that the species could have reached up to about 1.8 m TL and lived up to 37 years old in age

Functional Connectivity of the Raphe Nuclei: Link to Tobacco Withdrawal in Smokers.

BackgroundAlthough nicotine alters serotonergic neurochemistry, clinical trials of serotonergic medications for smoking cessation have provided mixed results. Understanding the role of serotonergic dysfunction in tobacco use disorder may advance development of novel pharmacotherapies.MethodsFunctional magnetic resonance imaging was used to measure resting-state functional connectivity of the raphe nuclei as an indicator of serotonergic function. Connectivity of the dorsal and median raphe nuclei was compared between 18 young smokers (briefly abstinent, ~40 minutes post-smoking) and 19 young nonsmokers (16-21 years old); connectivity was also examined in a separate sample of overnight-abstinent smokers (18-25 years old), before and after smoking the first cigarette of the day. Relationships between connectivity of the raphe nuclei with psychological withdrawal and craving were tested in smokers.ResultsConnectivity of the median raphe nucleus with the right hippocampal complex was weaker in smokers than in nonsmokers and was negatively correlated with psychological withdrawal in smokers. In overnight-abstinent smokers, smoking increased connectivity of the median raphe nucleus with the right hippocampal complex, and the increase was positively correlated with the decrease in psychological withdrawal.ConclusionsRelief of withdrawal due to smoking is potentially linked to the serotonergic pathway that includes the median raphe nucleus and hippocampal complex. These results suggest that serotonergic medications may be especially beneficial for smokers who endorse strong psychological withdrawal during abstinence from smoking

Forty-five year apart: Confronting the legacy of racial discrimination at the University of Cape Town

One of the many consequences of South Africa's history of racial discrimination is the impact it had on the training of black medical students. Blacks, and particularly those classified as African under apartheid’s racial classification, were restricted from entry to medical schools by a permit system introduced in 1959 and only rescinded in 1986.1 In 1967, the ratio of white doctors trained per million of the white population in South Africa was almost 100 times higher than the equivalent ratio for Africans,2 and although whites constituted less than 20% of the population, 83% of all doctors and 94% of all specialists in South Africa in 1985 were white.3 Not only were blacks largely excluded from training opportunities but, for those gaining access to medical schools, the conditions under which they trained were extremely onerous, and lacked the educational, recreational, accommodation and social opportunities afforded their white colleagues.1,2,4,5 A comment by a leading academic in 1988 on the state of medical training could have been applied to almost all of South Africa’s medical schools during apartheid: ‘. . . in spite of our much vaunted Academic Freedom, our policy and practice is heavily influenced, if not determined, by . . . an oppressive apartheid ideology. Why else have we produced so few African doctors; why else does the University . . . not have a satisfactory teaching hospital or residence for its [African] students?