Ultra-high temperature stability Joule-Thomson cooler with capability to accomodate pressure variations

A Joule-Thomson cryogenic refrigeration system capable of achieving high temperature stabilities in the presence of varying temperature, atmospheric pressure, and heat load is provided. The Joule-Thomson cryogenic refrigeration system includes a demand flow Joule-Thomson expansion valve disposed in a cryostat of the refrigeration system. The expansion valve has an adjustable orifice that controls the flow of compressed gas therethrough and induces cooling and partial liquefaction of the gas. A recuperative heat exchanger is disposed in the cryostat and coupled to the expansion valve. A thermostatically self-regulating mechanism is disposed in the cryostat and coupled to the J-T expansion valve. The thermostatically self-regulating mechanism automatically adjusts the cross sectional area of the adjustable valve orifice in response to environmental temperature changes and changes in power dissipated at a cold head. A temperature sensing and adjusting mechanism is coupled to a cold head for adjusting the temperature of the cold head in response to the change in heat flow in the cold head. The temperature sensing and adjusting mechanism comprises a temperature sensitive diode, a wound wire heater, and an electrical feedback control circuit coupling the diode to the heater. An absolute pressure relief valve is interposed between the output of the cryostat and an exhaust port for maintaining a constant exhaust temperature in the refrigerating system, independent of the changes in atmospheric pressure

Estimating the Returns to Insider Trading

This paper estimates the returns to insiders when they trade their company’s stock. We first construct a rolling "purchase portfolio" that holds all shares purchased by insiders for a six-month period, and an analogous "sale portfolio" that holds all shares sold by insiders for six months. The six-month horizon is chosen to coincide with the "short-swing" rule of the Securities and Exchange Act of 1934; a rule that prohibits profit-taking by insiders for offsetting trades within six months. We then employ performance-evaluation methods to analyze the returns to the purchase and sale portfolios. This approach yields a proxy for the value-weighted returns to insider transactions beginning on the day after their execution and avoids the statistical difficulties that plague event studies on long-horizon returns. Our methods are designed to estimate the returns earned by insiders themselves and thereby differ from the previous insider-trading literature, which focuses on the "informativeness" of insider trades for other investors. Using a comprehensive sample of reported insider transactions from 1975-1996, we find that the purchase portfolio earns abnormal returns of more than 50 basis points per month. About one-quarter of these abnormal returns accrue within the first five days after the initial transaction, and one-half accrue within the first month. The sale portfolio does not earn abnormal returns. Our portfolio-based approach also allows for straightforward decompositions of performance by various characteristics; we find that the abnormal returns to insider trades in small firms are not significantly different from those in large firms, and that top executives do not earn higher abnormal returns than do other insiders.

Higher Order and boundary Scaling Fields in the Abelian Sandpile Model

The Abelian Sandpile Model (ASM) is a paradigm of self-organized criticality (SOC) which is related to $c=-2$ conformal field theory. The conformal fields corresponding to some height clusters have been suggested before. Here we derive the first corrections to such fields, in a field theoretical approach, when the lattice parameter is non-vanishing and consider them in the presence of a boundary.Comment: 7 pages, no figure

The para-substituent effect and pH-dependence of the organometallic Baeyer–Villiger oxidation of rhenium–carbon bonds

We studied the Baeyer–Villiger (BV) type oxidation of phenylrhenium trioxide (PTO) by H2O2 in the aqueous phase using Quantum Mechanics (density functional theory with the M06 functional) focusing on how the solution pH and the para-substituent affect the Gibbs free energy surfaces. For both PTO and MTO (methylrhenium trioxide) cases, we find that for pH > 1 the BV pathway having OH− as the leaving group is lower in energy than the one involving simultaneous protonation of hydroxide. We also find that during this organometallic BV oxidation, the migrating phenyl is a nucleophile so that substituting functional groups in the para-position of phenyl with increased electron-donating character lowers the migration barrier, just as in organic BV reactions. However, this substituent effect also pushes electron density to Re, impeding HOO− coordination and slowing down the reaction. This is in direct contrast to the organic analog, in which para-substitution has an insignificant influence on 1,2-addition of peracids. Due to the competition of the two opposing effects and the dependence of the resting state on pH and concentration, the reaction rate of the organometallic BV oxidation is surprisingly unaffected by para-substitution

A selected history of expectation bias in physics

The beliefs of physicists can bias their results towards their expectations in a number of ways. We survey a variety of historical cases of expectation bias in observations, experiments, and calculations.Comment: 6 pages, 2 figure