On-Line Learning with Restricted Training Sets: An Exactly Solvable Case

We solve the dynamics of on-line Hebbian learning in large perceptrons exactly, for the regime where the size of the training set scales linearly with the number of inputs. We consider both noiseless and noisy teachers. Our calculation cannot be extended to non-Hebbian rules, but the solution provides a convenient and welcome benchmark with which to test more general and advanced theories for solving the dynamics of learning with restricted training sets.Comment: 19 pages, eps figures included, uses epsfig macr

Evaluation of enzyme immunoassays in the diagnosis of camel (Camelus dromedarius) trypanosomiasis:a preliminary investigation

Three enzyme immunoassays were used for the serodiagnosis of Trypanosoma evansi in camels in the Sudan in order to evaluate their ability to discriminate between infected and non-infected animals. Two assays were used for the detection of trypanosomal antibodies, one using specific anti-camel IgG conjugate and another using a non-specific Protein A conjugate. The third assay detected the presence of trypanosomal antigens using anti-T. evansi antibodies in a double antibody sandwich assay. Inspection of the frequency distribution of assay results suggested that the ELISA for circulating trypanosomal antibodies using specific antisera and the ELISA for circulating antigens can distinguish between non-infected camels and infected camels exhibiting patent infections or not. The ELISA using Protein A conjugate to bind non-specifically to camel immunoglobulin did not appear to discriminate between infected and non-infected animals

Pharmacist intervention in primary care to improve outcomes in patients with left ventricular systolic dysfunction

<b>Background</b> Meta-analysis of small trials suggests that pharmacist-led collaborative review and revision of medical treatment may improve outcomes in heart failure.<p></p> <b>Methods and results</b> We studied patients with left ventricular systolic dysfunction in a cluster-randomized controlled, event driven, trial in primary care. We allocated 87 practices (1090 patients) to pharmacist intervention and 87 practices (1074 patients) to usual care. The intervention was delivered by non-specialist pharmacists working with family doctors to optimize medical treatment. The primary outcome was a composite of death or hospital admission for worsening heart failure. This trial is registered, number ISRCTN70118765. The median follow-up was 4.7 years. At baseline, 86% of patients in both groups were treated with an angiotensin-converting enzyme inhibitor or an angiotensin receptor blocker. In patients not receiving one or other of these medications, or receiving less than the recommended dose, treatment was started, or the dose increased, in 33.1% of patients in the intervention group and in 18.5% of the usual care group [odds ratio (OR) 2.26, 95% CI 1.64–3.10; P< 0.001]. At baseline, 62% of each group were treated with a β-blocker and the proportions starting or having an increase in the dose were 17.9% in the intervention group and 11.1% in the usual care group (OR 1.76, 95% CI 1.31–2.35; P< 0.001). The primary outcome occurred in 35.8% of patients in the intervention group and 35.4% in the usual care group (hazard ratio 0.97, 95% CI 0.83–1.14; P = 0.72). There was no difference in any secondary outcome.<p></p> <b>Conclusion</b> A low-intensity, pharmacist-led collaborative intervention in primary care resulted in modest improvements in prescribing of disease-modifying medications but did not improve clinical outcomes in a population that was relatively well treated at baseline

Laser cooling of a nanomechanical resonator mode to its quantum ground state

We show that it is possible to cool a nanomechanical resonator mode to its ground state. The proposed technique is based on resonant laser excitation of a phonon sideband of an embedded quantum dot. The strength of the sideband coupling is determined directly by the difference between the electron-phonon couplings of the initial and final states of the quantum dot optical transition. Possible applications of the technique we describe include generation of non-classical states of mechanical motion.Comment: 5 pages, 3 figures, revtex

Quantum Theory of Cavity-Assisted Sideband Cooling of Mechanical Motion

We present a fully quantum theory describing the cooling of a cantilever coupled via radiation pressure to an illuminated optical cavity. Applying the quantum noise approach to the fluctuations of the radiation pressure force, we derive the opto-mechanical cooling rate and the minimum achievable phonon number. We find that reaching the quantum limit of arbitrarily small phonon numbers requires going into the good cavity (resolved phonon sideband) regime where the cavity linewidth is much smaller than the mechanical frequency and the corresponding cavity detuning. This is in contrast to the common assumption that the mechanical frequency and the cavity detuning should be comparable to the cavity damping.Comment: 5 pages, 2 figure

Constraining quasar host halo masses with the strength of nearby Lyman-alpha forest absorption

Using cosmological hydrodynamic simulations we measure the mean transmitted flux in the Lyman alpha forest for quasar sightlines that pass near a foreground quasar. We find that the trend of absorption with pixel-quasar separation distance can be fitted using a simple power law form including the usual correlation function parameters r_{0} and \gamma so that ( = \sum exp(-tau_eff*(1+(r/r_{0})^(-\gamma)))). From the simulations we find the relation between r_{0} and quasar mass and formulate this as a way to estimate quasar host dark matter halo masses, quantifying uncertainties due to cosmological and IGM parameters, and redshift errors. With this method, we examine data for ~3000 quasars from the Sloan Digital Sky Survey (SDSS) Data Release 3, assuming that the effect of ionizing radiation from quasars (the so-called transverse proximity effect) is unimportant (no evidence for it is seen in the data.) We find that the best fit host halo mass for SDSS quasars with mean redshift z=3 and absolute G band magnitude -27.5 is log10(M/M_sun) = 12.48^{+0.53}_{-0.89}. We also use the Lyman-Break Galaxy (LBG) and Lyman alpha forest data of Adelberger et al in a similar fashion to constrain the halo mass of LBGs to be log10(M/M_sun) = 11.13^{+0.39}_{-0.55}, a factor of ~20 lower than the bright quasars. In addition, we study the redshift distortions of the Lyman alpha forest around quasars, using the simulations. We use the quadrupole to monopole ratio of the quasar-Lyman alpha forest correlation function as a measure of the squashing effect. We find that this does not have a measurable dependence on halo mass, but may be useful for constraining cosmic geometry.Comment: 10 pages, 11 figures, submitted to MNRA

First Order Premelting Transition of Vortex Lattices

Vortex lattices in the high temperature superconductors undergo a first order phase transition which has thus far been regarded as melting from a solid to a liquid. We point out an alternative possibility of a two step process in which there is a first order transition from an ordinary vortex lattice to a soft vortex solid followed by another first order melting transition from the soft vortex solid to a vortex liquid. We focus on the first step. This premelting transition is induced by vacancy and interstitial vortex lines. We obtain good agreement with the experimental transition temperature versus field, latent heat, and magnetization jumps for YBCO and BSCCO.Comment: revised version replaces 9705092, 5 pages, Latex, 2 postscript figures, defect line wandering is included, 2 step melting is propose

Interaction of Agulhas filaments with mesoscale turbulence: a case study

The inter-ocean leakage of heat and salt from the South Indian Ocean to the South Atlantic has important consequences for the global thermohaline circulation and in particular for the strength of overturning of the Atlantic Ocean as a whole. This leakage between these two subtropical gyres takes place south of Africa. The main mechanisms are the intermittent shedding of Agulhas rings from the retroflection of the Agulhas Current and the advection of Agulhas filaments from the border of the Agulhas Current, both of which move northwestward into the South Atlantic. The subsequent behaviour and mixing of Agulhas rings has been much studied over the past years, that of Agulhas filaments not at all. We report here on fortuitous hydrographic observations of the behaviour of an Agulhas filament that interacted with a number of mesoscale features shortly after formation. This suggests that Agulhas filaments may be involved in many other circulation elements and not only the Benguela upwelling front, as was surmised previously, and may mix out in a very site-specific region

Utilitarian Collective Choice and Voting

In his seminal Social Choice and Individual Values, Kenneth Arrow stated that his theory applies to voting. Many voting theorists have been convinced that, on account of Arrow’s theorem, all voting methods must be seriously flawed. Arrow’s theory is strictly ordinal, the cardinal aggregation of preferences being explicitly rejected. In this paper I point out that all voting methods are cardinal and therefore outside the reach of Arrow’s result. Parallel to Arrow’s ordinal approach, there evolved a consistent cardinal theory of collective choice. This theory, most prominently associated with the work of Harsanyi, continued the older utilitarian tradition in a more formal style. The purpose of this paper is to show that various derivations of utilitarian SWFs can also be used to derive utilitarian voting (UV). By this I mean a voting rule that allows the voter to score each alternative in accordance with a given scale. UV-k indicates a scale with k distinct values. The general theory leaves k to be determined on pragmatic grounds. A (1,0) scale gives approval voting. I prefer the scale (1,0,-1) and refer to the resulting voting rule as evaluative voting. A conclusion of the paper is that the defects of conventional voting methods result not from Arrow’s theorem, but rather from restrictions imposed on voters’ expression of their preferences. The analysis is extended to strategic voting, utilizing a novel set of assumptions regarding voter behavior