Social Work handbook

1999 handbook for the Board of Studies in Social Wor

Mesoscopic Aharonov-Bohm oscillations in metallic rings

We study the amplitude of mesoscopic Aharonov-Bohm oscillations in quasi-one-dimensional (Q1D) diffusive rings. We consider first the low-temperature limit of a fully coherent sample. The variance of oscillation harmonics is calculated as a function of the length of the leads attaching the ring to reservoirs. We further analyze the regime of relatively high temperatures, when the dephasing due to electron-electron interaction suppresses substantially the oscillations. We show that the dephasing length L_phi^AB governing the damping factor exp(-2pi R /L_phi^AB) of the oscillations is parametrically different from the common dephasing length for the Q1D geometry. This is due to the fact that the dephasing is governed by energy transfers determined by the ring circumference 2pi R, making L_phi^AB R-dependent.Comment: 16 pages, 4 figures, to appear in proceedings of NATO/Euresco Conference "Fundamental Problems of Mesoscopic Physics: Interactions and Decoherence", Granada (Spain), September 200

Decoupling of Degenerate Positive-norm States in Witten's String Field Theory

We show that the degenerate positive-norm physical propagating fields of the open bosonic string can be gauged to the higher rank fields at the same mass level. As a result, their scattering amplitudes can be determined from those of the higher spin fields. This phenomenon arises from the existence of two types of zero-norm states with the same Young representations as those of the degenerate positive-norm states in the old covariant first quantized (OCFQ) spectrum. This is demonstrated by using the lowest order gauge transformation of Witten's string field theory (WSFT) up to the fourth massive level (spin-five), and is found to be consistent with conformal field theory calculation based on the first quantized generalized sigma-model approach. In particular, on-shell conditions of zero-norm states in OCFQ stringy gauge transformation are found to correspond, in a one-to-one manner, to the background ghost fields in off-shell gauge transformation of WSFT. The implication of decoupling of scalar modes on Sen's conjectures was also briefly discussed.Comment: 18 pages, use Latex with revtex

Chaotic inflation in Jordan frame supergravity

We consider the inflationary scenario with non-minimal coupling in 4D Jordan frame supergravity. We find that there occurs a tachyonic instability along the direction of the accompanying non-inflaton field in generic Jordan frame supergravity models. We propose a higher order correction to the Jordan frame function for solving the tachyonic mass problem and show that the necessary correction can be naturally generated by the heavy thresholds without spoiling the slow-roll conditions. We discuss the implication of the result on the Higgs inflation in NMSSM.Comment: 16 pages, no figures, version to be published in JCA

Quantum dots with two electrons: Singlet-triplet transitions

The magnetic character of the ground-state of two electrons on a double quantum dot, connected in series to left and right single-channel leads, is considered. By solving exactly for the spectrum of the two interacting electrons, it is found that the coupling to the continuum of propagating states on the leads, in conjunction with the electron-electron interactions, may result in a delocalization of the bound state of the two electrons. This, in turn, reduces significantly the range of the Coulomb interaction parameters over which singlet-triplet transitions can be realized. It is also found that the coupling to the leads favors the singlet ground-state.Comment: 8 pages, submitted to Phys. Rev.

Towards the development of an Inter-Cultural Scale to Measure Trust in Automation

Trust is conceived as an attitude leading to intentions resulting in user actions involving automation. It is generally believed that trust is dynamic and that a user’s prior experience with automation affects future behavior indirectly through causing changes in trust. Additionally, individual differences and cultural factors have been frequently cited as the contributors to influencing trust beliefs about using and monitoring automation. The presented research focuses on modeling human’s trust when interacting with automated systems across cultures. The initial trust assessment instrument, comprising 110 items along with 2 perceptions (general vs. specific use of automation), has been empirically validated. Detailed results comparing items and dimensionality with our new pooled measure will be presented

Higher spins dynamics in the closed string theory

The general $\sigma$-model-type string action including both massless and massive higher spins background fields is suggested. Field equations for background fields are followed from the requirement of quantum Weyl invariance. It is shown that renormalization of the theory can be produced level by level. The detailed consideration of background fields structure and corresponding fields equations is given for the first massive level of the closed bosonic string.Comment: 11 pages, report TSU/QFTD-36/9

Interaction corrections at intermediate temperatures: dephasing time

We calculate the temperature dependence of the weak localization correction in a two dimensional system at arbitrary relation between temperature, $T$ and the elastic mean free time. We describe the crossover in the dephasing time ${\tau_\phi(T)}$ between the high temperature, $1/\tau_\phi \simeq T^2 \ln T$, and the low temperature $1/\tau_\phi \simeq T$ behaviors. The prefactors in these dependences are not universal, but are determined by the Fermi liquid constant characterising the spin exchange interaction.Comment: 4 pages, to appear in PRB, minor errors corrected, added reference

Conductance fluctuations in the presence of spin scattering

Electron transport through disordered systems that include spin scatterers is studied numerically. We consider three kinds of magnetic impurities: the Ising, the XY and the Heisenberg. By extending the transfer matrix method to include the spin degree of freedom, the two terminal conductance is calculated. The variance of conductance is halved as the number of spin components of the magnetic impurities increases. Application of the Zeeman field in the lead causes a further halving of the variance under certain conditions.Comment: to be published in Phys. Rev.

Radionuclide Contaminant Burdens in Arctic Marine Mammals Harvested During Subsistence Hunting

We conducted gamma spectrometric analyses on more than 200 arctic marine mammal tissue samples. These samples were primarily provided by subsistence hunters from northern Alaska, with a smaller number of samples from the Resolute region in Canada. The majority of samples (>90%) had detectable levels of the anthropogenic radionuclide 137Cs, with a mean level observed in all samples of 0.67 Bq/kg dry weight ± 0.81 (SD). Converted to wet weight, the mean was 0.21 Bq/kg ± 0.19 SD. The median activity observed was 0.45 Bq/kg dry weight (0.18 Bq/kg wet weight) with a range from detection limits to 6.7 Bq/kg dry weight (1.1 Bq/kg wet weight). These findings confirm expectations that current anthropogenic gamma emitter burdens in marine mammals used in the North American Arctic as subsistence food resources are well below activities that would normally merit public health concern (~1000 Bq/kg wet weight). Some differences among species and tissues were observed. Beluga tissues had slightly higher mean burdens of 137Cs overall, and epidermis and muscle tissues in bowhead and beluga whales typically had higher burdens than other tissues analyzed. Low levels of the neutron activation product 108mAg (half-life 418 yr.), probably bioaccumulated from bomb fallout sources, were observed in 16 of 17 beluga livers analyzed, but were not found in any other tissues of beluga or in any other species sampled. A subset of 39 samples of various tissues was analyzed for the alpha and beta emitters 239,240Pu and 90Sr. Plutonium levels were near the threshold of detectability (~0.1 Bq/kg dry weight) in 6 of the 39 samples; all other samples had no detectable plutonium. A detectable level of 90Sr (10.3 ± 1.0 Bq/kg dry weight) was observed in only one of the 39 samples analyzed, a bowhead epidermis sample. Although the accumulation of 108mAg has not been previously reported in any marine mammal livers, all of our analytical measurements indicate that only very low levels of anthropogenic radioactivity are associated with marine mammals harvested and consumed in the North American Arctic.On a effectué des analyses gamma-spectrométriques sur plus de 200 échantillons de tissus prélevés sur des mammifères marins. La plupart de ces échantillons étaient fournis par des chasseurs de subsistance de l'Alaska septentrional, et un petit nombre venaient de la région de Resolute au Canada. La majorité des échantillons (> 90 p. cent) contenaient des niveaux détectables du radionucléide anthropique 137Cs, avec un niveau moyen observé dans tous les échantillons de 0,67 Bq/kg de poids sec ± 0,81 (écart-type). Convertie en poids frais, la moyenne était de 0,21 Bq/kg ± 0,19 d'écart-type. L'activité médiane observée était de 0,45 Bq/kg de poids sec (0,18 Bq/kg de poids frais) avec une fourchette allant des seuils de détection jusqu'à 6,7 Bq/kg de poids sec (1,1 Bq/kg de poids frais). Ces résultats confirment les réponses prévues, à savoir que les charges actuelles des émetteurs gamma anthropiques présentes chez les mammifères marins utilisés en Amérique du Nord comme ressource de subsistance sont bien inférieures aux niveaux qui voudraient normalement qu'on s'inquiète pour la santé publique (~1000 Bq/kg de poids frais). On a observé certaines différences dans les espèces et les tissus. Dans l'ensemble, les tissus prélevés sur le bélouga contenaient des charges moyennes de 137Cs légèrement plus élevées, et l'épiderme et les tissus musculaires de la baleine boréale et du bélouga avaient généralement des charges supérieures à celles trouvées dans les autres tissus analysés. Dans 16 des 17 foies de bélouga analysés, on a observé de faibles niveaux du produit d'activation neutronique 108mAg (demi-vie 418 années), dont la bioaccumulation est probablement due à des retombées de bombes atomiques, mais on n'en a observé aucune trace dans les autres tissus du bélouga ou de toute autre espèce échantillonnée. On a analysé un sous-ensemble de 39 échantillons provenant de tissus divers pour savoir s'ils contenaient des émetteurs alpha et bêta 239,240Pu et 90Sr. Dans 6 des 39 échantillons, les niveaux de plutonium étaient proches du seuil de détectabilité (~ 0,1 Bq/kg de poids sec), et on n'a pas trouvé de plutonium détectable dans aucun des autres échantillons. On a observé un niveau détectable de 90Sr (10,3 ± 1,0 Bq/kg de poids sec) dans un seul des 39 échantillons analysés, soit un échantillon d'épiderme de baleine boréale. Bien qu'on n'ait jamais rapporté auparavant une accumulation de 108mAg dans le foie d'un mammifère marin, toutes nos mesures analytiques révèlent que les mammifères marins faisant l'objet d'une activité d'exploitation et consommés dans l'Arctique nord-américain ne présentent que de très faibles niveaux de radioactivité anthropique