The Formation of Fragments at Corotation in Isothermal Protoplanetary Disks

Numerical hydrodynamics simulations have established that disks which are evolved under the condition of local isothermality will fragment into small dense clumps due to gravitational instabilities when the Toomre stability parameter $Q$ is sufficiently low. Because fragmentation through disk instability has been suggested as a gas giant planet formation mechanism, it is important to understand the physics underlying this process as thoroughly as possible. In this paper, we offer analytic arguments for why, at low $Q$, fragments are most likely to form first at the corotation radii of growing spiral modes, and we support these arguments with results from 3D hydrodynamics simulations.Comment: 21 pages, 1 figur

An Australian twin study of cannabis and other illicit drug use and misuse, and other psychopathology

Cannabis is the most widely used illicit drug throughout the developed world and there is consistent evidence of heritable influences on multiple stages of cannabis involvement including initiation of use and abuse/dependence. In this paper, we describe the methodology and preliminary results of a large-scale interview study of 3,824 young adult twins (born 1972–1979) and their siblings. Cannabis use was common with 75.2% of males and 64.7% of females reporting some lifetime use of cannabis while 24.5% of males and 11.8% of females reported meeting criteria for DSM-IV cannabis abuse or dependence. Rates of other drug use disorders and common psychiatric conditions were highly correlated with extent of cannabis involvement and there was consistent evidence of heritable influences across a range of cannabis phenotypes including early (≤15 years) opportunity to use (h(2) = 72%), early (≤16 years) onset use (h(2) = 80%), using cannabis 11+ times lifetime (h(2) = 76%), and DSM abuse/dependence (h(2) = 72%). Early age of onset of cannabis use was strongly associated with increased rates of subsequent use of other illicit drugs and with illicit drug abuse/dependence; further analyses indicating that some component of this association may have been mediated by increasing exposure to and opportunity to use other illicit drugs

Simultaneous Diagonal and Off Diagonal Order in the Bose--Hubbard Hamiltonian

The Bose-Hubbard model exhibits a rich phase diagram consisting both of insulating regimes where diagonal long range (solid) order dominates as well as conducting regimes where off diagonal long range order (superfluidity) is present. In this paper we describe the results of Quantum Monte Carlo calculations of the phase diagram, both for the hard and soft core cases, with a particular focus on the possibility of simultaneous superfluid and solid order. We also discuss the appearance of phase separation in the model. The simulations are compared with analytic calculations of the phase diagram and spin wave dispersion.Comment: 28 pages plus 24 figures, uuencoded Revtex+postscript file

Simulation models for tankless gas water heaters

There is a growing concern about to the scarceness of natural resources and the emissions problematic. Water heating is a relevant part of a household’s energy use, and tankless gas water heaters (TGWH) are widely used. There are design and engineering challenges to develop more efficient devices, with lower emissions of pollutant gases and providing comfort improvements from the user point of view. The main objective of the present work is to provide mathematical models to evaluate and support the development of different TGWH configurations. By simulation, different hardware configurations and advanced control strategies can be tested and optimized regarding energy saving, reducing of harmful environmental emissions and increase of comfort indices by reducing temperature undershoots and overshoots. The TGWH individual components are modelled, laboratory tests are performed and the heat cell is parametrized with experimental data. Configurations with and without bypass function are performed for several water flow rates and setpoint temperature patterns in open loop and with feed-forward control.publishe

Hydrodynamics of Spatially Ordered Superfluids

We derive the hydrodynamic equations for the supersolid and superhexatic phases of a neutral two-dimensional Bose fluid. We find, assuming that the normal part of the fluid is clamped to an underlying substrate, that both phases can sustain third-sound modes and that in the supersolid phase there are additional modes due to the superfluid motion of point defects (vacancies and interstitials).Comment: 24 pages of ReVTeX and 7 uuencoded figures. Submitted for publication in Phys. Rev.

Forming a stable memory representation in the first year of life: Why imitation is more than child's play.

Although 9-month-old infants are capable of retaining temporally ordered information over long delays, this ability is relatively fragile. It may be possible to facilitate long-term retention by allowing infants to imitate event sequences immediately after their presentation. The effects of imitation on immediate and delayed recognition and on long-term recall were investigated using event-related potentials (ERPs) and elicited imitation, respectively. Mnemonic facilitation resulting from the opportunity to imitate was apparent using both assessments. ERP assessments at immediate and delayed recognition tests suggested that infants who were allowed to imitate had stronger memory representations of familiar stimuli relative to infants who only viewed the presentation of the events. In addition, infants who were allowed to imitate evidenced higher levels of ordered recall after 1 month relative to infants who only watched the experimenter’s demonstration. Therefore, imitation proved to have beneficial effects on explicit memory in 9 1 / 2 -month-olds, providing evidence of its effectiveness as a tool to augment mnemonic capabilities in infancy

Quantum Phase Transitions and Conserved Charges

The constraints on the scaling properties of conserved charge densities in the vicinity of a zero temperature ($T$), second-order quantum phase transition are studied. We introduce a generalized Wilson ratio, characterizing the non-linear response to an external field, $H$, coupling to any conserved charge, and argue that it is a completely universal function of $H/T$: this is illustrated by computations on model systems. We also note implications for transitions where the order parameter is a conserved charge (as in a $T=0$ ferromagnet-paramagnet transition).Comment: 19 pages, REVTEX 3.0, 8 uuencoded Postscript figues appended, YCTP-xxx

Andreev reflections in the pseudogap state of cuprate supercondcutors

We propose that, if the pseudogap state in the cuprate superconductors can be described in terms of the phase-incoherent preformed pairs, there should exist Andreev reflection from these pairs even above the superconducting transition temperature, $T_c$. After giving qualitative arguments for this effect, we present more quantitative calculations based on the Bogoliubov--de Gennes equation. Experimental observations of the effects of Andreev reflections above $T_c$---such as an enhanced tunneling conductance below the gap along the copper oxide plane---could provide unambiguous evidence for the preformed pairs in the pseudogap state.Comment: 5 pages, 1 figur