463 research outputs found
Free recall test experience potentiates strategy-driven effects of value on memory.
People tend to show better memory for information that is deemed valuable or important. By one mechanism, individuals selectively engage deeper, semantic encoding strategies for high value items (Cohen, Rissman, Suthana, Castel, & Knowlton, 2014). By another mechanism, information paired with value or reward is automatically strengthened in memory via dopaminergic projections from midbrain to hippocampus (Shohamy & Adcock, 2010). We hypothesized that the latter mechanism would primarily enhance recollection-based memory, while the former mechanism would strengthen both recollection and familiarity. We also hypothesized that providing interspersed tests during study is a key to encouraging selective engagement of strategies. To test these hypotheses, we presented participants with sets of words, and each word was associated with a high or low point value. In some experiments, free recall tests were given after each list. In all experiments, a recognition test was administered 5 minutes after the final word list. Process dissociation was accomplished via remember/know judgments at recognition, a recall test probing both item memory and memory for a contextual detail (word plurality), and a task dissociation combining a recognition test for plurality (intended to probe recollection) with a speeded item recognition test (to probe familiarity). When recall tests were administered after study lists, high value strengthened both recollection and familiarity. When memory was not tested after each study list, but rather only at the end, value increased recollection but not familiarity. These dual process dissociations suggest that interspersed recall tests guide learners' use of metacognitive control to selectively apply effective encoding strategies. (PsycINFO Database Recor
Spectrum of surface-mode contributions to the excitation probability for electron beam interacting with sharp-edged dielectric wedges
The interaction of a nonrelativistic charged particle beam, travelling
parallel to the surface of a sharp-edged dielectric wedge is analyzed. The
general expressions for excitation probability are obtained for a beam moving
along the direction of a symmetry axis, either outside or inside the dielectric
wedge. The dielectric function of the medium is assumed to be isotropic, and
numerical results are given for the materials of experimental interest.Comment: LaTeX 2.09, 15 pages, 10 figure
Optimal refrigerator
We study a refrigerator model which consists of two -level systems
interacting via a pulsed external field. Each system couples to its own thermal
bath at temperatures and , respectively ().
The refrigerator functions in two steps: thermally isolated interaction between
the systems driven by the external field and isothermal relaxation back to
equilibrium. There is a complementarity between the power of heat transfer from
the cold bath and the efficiency: the latter nullifies when the former is
maximized and {\it vice versa}. A reasonable compromise is achieved by
optimizing the product of the heat-power and efficiency over the Hamiltonian of
the two system. The efficiency is then found to be bounded from below by
(an analogue of the Curzon-Ahlborn
efficiency), besides being bound from above by the Carnot efficiency
. The lower bound is reached in the
equilibrium limit . The Carnot bound is reached (for a finite
power and a finite amount of heat transferred per cycle) for . If
the above maximization is constrained by assuming homogeneous energy spectra
for both systems, the efficiency is bounded from above by and
converges to it for .Comment: 12 pages, 3 figure
Coherence as ultrashort pulse train generator
Intense, well-controlled regular light pulse trains start to play a crucial
role in many fields of physics. We theoretically demonstrate a very simple and
robust technique for generating such periodic ultrashort pulses from a
continuous probe wave which propagates in a dispersive thermal gas media
Magnetic and quantum entanglement properties of the distorted diamond chain model for azurite
We present the results of magnetic properties and entanglement of the
distorted diamond chain model for azurite using pure quantum exchange
interactions. The magnetic properties and concurrence as a measure of pairwise
thermal entanglement have been studied by means of variational mean-field like
treatment based on Gibbs-Bogoliubov inequality. Such a system can be considered
as an approximation of the natural material azurite, Cu3(CO3)2(OH)2. For values
of exchange parameters, which are taken from experimental results, we study the
thermodynamic properties, such as azurite specific heat and magnetic
susceptibility. We also have studied the thermal entanglement properties and
magnetization plateau of the distorted diamond chain model for azurite
Energy measurements remain thermometrically optimal beyond weak coupling
We develop a general perturbative theory of finite-coupling quantum thermometry up to second order in probe-sample interaction. By assumption, the probe and sample are in thermal equilibrium, so the probe is described by the mean-force Gibbs state. We prove that the ultimate thermometric precision can be achieved – to second order in the coupling – solely by means of local energy measurements on the probe. Hence, seeking to extract temperature information from coherences or devising adaptive schemes confers no practical advantage in this regime. Additionally, we provide a closed-form expression for the quantum Fisher information, which captures the probe's sensitivity to temperature variations. Finally, we benchmark and illustrate the ease of use of our formulas with two simple examples. Our formalism makes no assumptions about separation of dynamical timescales or the nature of either the probe or the sample. Therefore, by providing analytical insight into both the thermal sensitivity and the optimal measurement for achieving it, our results pave the way for quantum thermometry in setups where finite-coupling effects cannot be ignored
Enhancement of low-temperature thermometry by strong coupling
We consider the problem of estimating the temperature T of a very cold equilibrium sample. The temperature estimates are drawn from measurements performed on a quantum Brownian probe strongly coupled to it. We model this scenario by resorting to the canonical Caldeira-Leggett Hamiltonian and find analytically the exact stationary state of the probe for arbitrary coupling strength. In general, the probe does not reach thermal equilibrium with the sample, due to their nonperturbative interaction. We argue that this is advantageous for low-temperature thermometry, as we show in our model that (i) the thermometric precision at low T can be significantly enhanced by strengthening the probe-sampling coupling, (ii) the variance of a suitable quadrature of our Brownian thermometer can yield temperature estimates with nearly minimal statistical uncertainty, and (iii) the spectral density of the probe-sample coupling may be engineered to further improve thermometric performance. These observations may find applications in practical nanoscale thermometry at low temperatures—a regime which is particularly relevant to quantum technologies
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