The Discretionary Function Exception in the Second Circuit

In a society governed by the rule of law, what is the responsibility of a government to rectify its own errors when those errors injure its citizens? In the Anglo-American legal tradition, this question has been debated at least since the Magna Carta, and it remains a vexed one. The answer to this question is especially elusive with respect to governmentinflicted personal injuries remediable only with money damages, a form of liability rule that has always been subject to broad areas of immunity for government, for its officials, and for both. In the United States, federal and state laws have waived many of these immunities

Nuclear Pairing in the T=0 channel revisited

Recent published data on the isoscalar gap in symmetric nuclear matter using the Paris force and the corresponding BHF single particle dispersion are corrected leading to an extremely high proton-neutron gap of $\Delta \sim 8$ MeV at $\rho \sim 0.5\rho_0$. Arguments whether this value can be reduced due to screening effects are discussed. A density dependent delta interaction with cut off is adjusted so as to approximately reproduce the nuclear matter values with the Paris force.Comment: 4 pages, 4 figure

Dynamics of few-body states in a medium

Strongly interacting matter such as nuclear or quark matter leads to few-body bound states and correlations of the constituents. As a consequence quantum chromodynamics has a rich phase structure with spontaneous symmetry breaking, superconductivity, condensates of different kinds. All this appears in many astrophysical scenarios. Among them is the formation of hadrns during the early stage of the Universe, the structure of a neutron star, the formation of nuclei during a supernova explosion. Some of these extreme conditions can be simulated in heavy ion colliders. To treat such a hot and dense system we use the Green function formalism of many-body theory. It turns out that a systematic Dyson expansion of the Green functions leads to modified few-body equations that are capable to describe phase transitions, condensates, cluster formation and more. These equations include self energy corrections and Pauli blocking. We apply this method to nonrelativistic and relativistic matter. The latter one is treated on the light front. Because of the medium and the inevitable truncation of space, the few-body dynamics and states depend on the thermodynamic parameters of the medium.Comment: 3 pages, 2 figures, talk presented at the 19th European Conference on Few-Body System

Boson-Fermion pairing in a Boson-Fermion environment

Propagation of a Boson-Fermion (B-F) pair in a B-F environment is considered. The possibility of formation of stable strongly correlated B-F pairs, embedded in the continuum, is pointed out. The new Fermi gas of correlated B-F pairs shows a strongly modified Fermi surface. The interaction between like particles is neglected in this exploratory study. Various physical situations where our new pairing mechanism could be of importance are invoked.Comment: 8 pages, 8 figers, to be published in Phys. Rev.

VLF and HF Plasma Waves Associated with Spread-F Plasma Depletions Observed on the C/NOFS Satellite

The C/NOFS spacecraft frequently encounters structured plasma depletions associated with equatorial spread-F along its trajectory that varies between 401 km perigee and 867 km apogee in the low latitude ionosphere. We report two classes of plasma waves detected with the Vector Electric Field Investigation (VEFI) that appear when the plasma frequency is less than the electron gyro frequency, as is common in spread-F depletions where the plasma number density typically decreases below 10(exp 4)/cu cm. In these conditions, both broadband VLF waves with a clear cutoff at the lower hybrid frequency and broadband HF waves with a clear cutoff at the plasma frequency are observed. We interpret these waves as "hiss-type" emissions possibly associated with the flow of suprathermal electrons within the inter-hemispherical magnetic flux tubes. We also report evidence of enhanced wave "transients" sometimes embedded in the broader band emissions that are associated with lightning sferics detected within the depleted plasma regions that appear in both the VLF and HF data. Theoretical implications of these observations are discussed

Screening Effects on 1S0^1S_0 Pairing in Neutron Matter

The $^1S_0$ superfluidity of neutron matter is studied in the framework of the generalized Gorkov equation. The vertex corrections to the pairing interaction and the self-energy corrections are introduced and approximated on the same footing in the gap equation. A suppression of the pairing gap by more than 50% with respect to the BCS prediction is found, which deeply changes the scenario for the dynamical and thermal evolution of neutron stars.Comment: 5 pages, 5 figres, RevTeX4 styl

Estimating Electric Fields from Vector Magnetogram Sequences

Determining the electric field (E-field) distribution on the Sun's photosphere is essential for quantitative studies of how energy flows from the Sun's photosphere, through the corona, and into the heliosphere. This E-field also provides valuable input for data-driven models of the solar atmosphere and the Sun-Earth system. We show how Faraday's Law can be used with observed vector magnetogram time series to estimate the photospheric E-field, an ill-posed inversion problem. Our method uses a "poloidal-toroidal decomposition" (PTD) of the time derivative of the vector magnetic field. The PTD solutions are not unique; the gradient of a scalar potential can be added to the PTD E-field without affecting consistency with Faraday's Law. We present an iterative technique to determine a potential function consistent with ideal MHD evolution; but this E-field is also not a unique solution to Faraday's Law. Finally, we explore a variational approach that minimizes an energy functional to determine a unique E-field, similar to Longcope's "Minimum Energy Fit". The PTD technique, the iterative technique, and the variational technique are used to estimate E-fields from a pair of synthetic vector magnetograms taken from an MHD simulation; and these E-fields are compared with the simulation's known electric fields. These three techniques are then applied to a pair of vector magnetograms of solar active region NOAA AR8210, to demonstrate the methods with real data.Comment: 41 pages, 10 figure

Absorption spectrum of a weakly n-doped semiconductor quantum well

We calculate, as a function of temperature and conduction band electron density, the optical absorption of a weakly n-doped, idealized semiconductor quantum well. In particular, we focus on the absorption band due to the formation of a charged exciton. We conceptualize the charged exciton as an itinerant excitation intimately linked to the dynamical response of itinerant conduction band electrons to the appearance of the photo-generated valence band hole. Numerical results for the absorption in the vicinity of the exciton line are presented and the spectral weights associated with, respectively, the charged exciton band and the exciton line are analyzed in detail. We find, in qualitative agreement with experimental data, that the spectral weight of the charged exciton grows with increasing conduction band electron density and/or decreasing temperature at the expense of the exciton.Comment: 5 pages, 4 figure

Chemical Raman Enhancement of Organic Adsorbates on Metal Surfaces

Using a combination of first-principles theory and experiments, we provide a quantitative explanation for chemical contributions to surface-enhanced Raman spectroscopy for a well-studied organic molecule, benzene thiol, chemisorbed on planar Au(111) surfaces. With density functional theory calculations of the static Raman tensor, we demonstrate and quantify a strong mode-dependent modification of benzene thiol Raman spectra by Au substrates. Raman active modes with the largest enhancements result from stronger contributions from Au to their electron-vibron coupling, as quantified through a deformation potential, a well-defined property of each vibrational mode. A straightforward and general analysis is introduced that allows extraction of chemical enhancement from experiments for specific vibrational modes; measured values are in excellent agreement with our calculations.Comment: 5 pages, 4 figures and Supplementary material included as ancillary fil