6,843 research outputs found
From Chemistry to Functionality: Trends for the Length Dependence of the Thermopower in Molecular Junctions
We present a systematic ab-initio study of the length dependence of the
thermopower in molecular junctions. The systems under consideration are small
saturated and conjugated molecular chains of varying length attached to gold
electrodes via a number of different binding groups. Different scenarios are
observed: linearly increasing and decreasing thermopower as function of the
chain length as well as positive and negative values for the contact
thermopower. Also deviation from the linear behaviour is found. The trends can
be explained by details of the transmission, in particular the presence,
position and shape of resonances from gateway states. We find that these
gateway states do not only determine the contact thermopower, but can also have
a large influence on the length-dependence itself. This demonstrates that
simple models for electron transport do not apply in general and that chemical
trends are hard to predict. Furthermore, we discuss the limits of our approach
based on Density Functional Theory and compare to more sophisticated methods
like self-energy corrections and the GW theory
Atom-molecule theory of broad Feshbach resonances
We derive the atom-molecule theory for an atomic gas near a broad Feshbach
resonance, where the energy dependence of the atom-molecule coupling becomes
crucial for understanding experimental results. We show how our many-body
theory incorporates the two-atom physics exactly. In particular, we calculate
the magnetic moment of a two-component gas of ^{6}Li atoms for a wide range of
magnetic fields near the broad Feshbach resonance at about 834 Gauss. We find
excellent agreement with the experiment of Jochim et al. [Phys. Rev. Lett. 91,
240402 (2003)].Comment: 4 pages, 2 figure
Quantum annealing and the Schr\"odinger-Langevin-Kostin equation
We show, in the context of quantum combinatorial optimization, or quantum
annealing, how the nonlinear Schr\"odinger-Langevin-Kostin equation can
dynamically drive the system toward its ground state. We illustrate, moreover,
how a frictional force of Kostin type can prevent the appearance of genuinely
quantum problems such as Bloch oscillations and Anderson localization which
would hinder an exhaustive search.Comment: 5 pages, 4 figures. To appear on Physical Review
Crossover temperature of Bose-Einstein condensation in an atomic Fermi gas
We show that in an atomic Fermi gas near a Feshbach resonance the crossover
between a Bose-Einstein condensate of diatomic molecules and a Bose-Einstein
condensate of Cooper pairs occurs at positive detuning, i.e., when the
molecular energy level lies in the two-atom continuum. We determine the
crossover temperature as a function of the applied magnetic field and find
excellent agreement with the experiment of Regal et al. [Phys. Rev. Lett. 92,
040403 (2004)] that has recently observed this crossover temperature.Comment: 4 pages, 2 figure
Natural Disasters and Preferences for the Environment: Evidence from the Impressionable Years
Do generations affected by natural disasters during the critical years of adolescence and
early adulthood form different preferences towards the environment than generations who are
not? Consistent with the theories of social psychology, we show that an environmental shock
experienced during the impressionable years (18-25 years old) help shape positive environmental
preferences. Individuals tend not to change beliefs in response to natural disasters experienced
in other age ranges. Using information from the General Social Survey and World Values Survey,
we exploit yearly natural disasters variation both within the US and across countries to identify
these effects
Natural Disasters and Preferences for the Environment: Evidence from the Impressionable Years
Do generations a˙ected by natural disasters during the critical years of adolescence and early adulthood form di˙erent preferences towards the environment than generations who are not? Consistent with the theories of social psychology, we show that an environmental shock experienced during the impressionable years (18-25 years old) help shape positive environmental preferences. Individuals tend not to change beliefs in response to natural disasters experienced in other age ranges. Using information from the General Social Survey and World Values Survey, we exploit yearly natural disasters variation both within the US and across countries to identify these effects
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