Electric polarizability of nuclei from a longitudinal sum rule

The nuclear electric polarizability is theoretically analyzed using a sum rule derived from the longitudinal part of the forward Compton amplitude. Beyond the leading dipole contribution, this approach leads to the presence of potential-dependent terms that do not show up in previous analyses. The significance of these new contributions is illustrated by performing an explicit calculation for a proton-neutron system interacting via a separable potential.Comment: 9 pages, revtex. Minor changes, two references added. To appear in Nucl. Phys.

A Data-Driven Approach to Measure Web Site Navigability

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One-step growth and shaping by a dual plasma reactor of diamond nanocones arrays for the assembling of stable cold cathodes

Arrays of conical-shaped nanodiamond structures are formed on silicon substrate by a single-step CVD process from CH4/H-2 mixtures. The formation of these nanocones has been found to depend on interplay between growing and etching during the CVD process carried out in a dual-mode MW/RF plasma reactor. Morphology and structure of the conical-like systems can be controlled by varying the process parameters, and have been investigated by scanning electron microscopy (SEM), reflection high energy electron diffraction (RHEED) and micro-Raman spectroscopy. The Field Emission (FE) properties of different diamond nanocones arrays have been investigated and compared with those of analogous systems in order to assess the feasibility of the present nano-materials as electron emitters for cold cathodes. The FE behavior is discussed taking into account the structure of the different diamond nanocones

ARTICLES Information entropy and squeezing of quantum fluctuations

Quantum-mechanical entropies of position and momentum operators in a given state are shown to be reasonable and sensitive measures for squeezing of quantum fluctuations. It is shown to be true not only for states having Gaussian wave functions but also for more general, both pure and mixed, quantum states. A simple proof that the squeezing exhibited by the variance is always accompanied by a corresponding entropy reduction below the entropy vacuum level is given. These results show that the information entropy is not only a theoretically satisfactory concept but can also be useful as a tool for more practical quantum-optics applications. ͓S1050-2947͑97͒02609-7͔ PACS number͑s͒: 03.65. Bz, 42.50.Dv, 42.50.Lc, 03.65.Ca In quantum mechanics two noncommuting observables cannot be simultaneously measured with arbitrary precision. This fact, often called the Heisenberg uncertainty principle, is a fundamental restriction that is related neither to imperfections of the existing real-life measuring devices nor to the experimental errors of observation ͓1͔. It is rather the intrinsic property of the quantum state itself. Paradoxically enough, the uncertainty principle provides the only way to avoid many interpretational problems. It can also be used to make qualitative predictions in atomic physics, e.g., the size of the ground-state energy of an atom and the spread of the ground-state wave function ͓2͔. The uncertainty principle specified for given pairs of observables finds its mathematical manifestation as the uncertainty relations. The first rigorous derivation of the uncertainty relation from the quantum-mechanical formalism applied for the basic noncommuting observables, i.e., for the position and momentum (͓x ,p ͔ϭi;បϭ1), is due to Kennard ͓3͔ ͑see also the work of Robertson ͓4͔͒. This derivation, repeated in most textbooks on quantum mechanics ever since, leads to the celebrated inequality In fact, it can be considered as a simple consequence of the properties of the Fourier transform that connects the wave functions of the system in the position and momentum representation. In the above expression the fundamental quantum uncertainty inherently tied to the pair of noncommuting observables is measured by the variance of the corresponding Hermitian operators. For example, for x ϭx † , where ͗ ͘ denotes the averaging with respect to a given state. It should be noted, however, that the variance is not the only measure of quantum uncertainty that can be used to express the uncertainty principle. Being just the second central moment of the probability distribution, it gives only a rough characterization of the probability distribution that is not of the Gaussian shape. It is, of course, possible to introduce higher moments ͓5͔, but all of them considered separately still contain only a restricted amount of information about the spreading of the values around the mean value. It is now commonly recognized that in many cases the variances ͑or standard deviations͒ are not appropriate measures of the quantum uncertainty. There exist many physically interesting situations where using variances leads to inadequate descriptions. A much more satisfactory measure of quantum uncertainty is given by the information entropy of the given probability distribution. The advantages of the entropic approach have been thoroughly scrutinized ͓6͔. In quantum mechanics the probability distribution of position ͑for a pure state͒ is given by the squared modulus of the wave function P(x)ϭ͉(x)͉ 2 . The probability distribution of momentum is given by a similar expression P(p)ϭ͉(p)͉ 2 , where the wave function in the momentum representation (p) is known to be the Fourier transform of the wave function (x). Following Shannon's ideas, we can define the entropies of position S x ϭϪ͐ P(x)lnP(x)dx and momentum S p ϭϪ͐ P(p)lnP(p)dp, respectively. There exists a very deep and interesting inequality satisfied by the sum of the above-mentioned position and momentum entropies S x ϩS p ϭϪ ͵ ͉͑x͉͒ 2 ln͉͑x ͉͒ 2 dxϪ ͵ ͉͑ p͉͒ 2 ln͉͑ p ͉͒ 2 dp у1ϩln. ͑3͒ A conjecture that the wave function and its Fourier transform should satisfy this relation was made almost 40 years ago by Everett in his work devoted to many-worlds interpretation of quantum mechanics ͓7͔ and independently by Hirschman ͓8

Inertial bioluminescence rhythms at the Capo Passero (KM3NeT-Italia) site, Central Mediterranean Sea

In the deep sea, the sense of time is dependent on geophysical fluctuations, such as internal tides and atmospheric-related inertial currents, rather than day-night rhythms. Deep-sea neutrino telescopes instrumented with light detecting Photo-Multiplier Tubes (PMT) can be used to describe the synchronization of bioluminescent activity of abyssopelagic organisms with hydrodynamic cycles. PMT readings at 8 different depths (from 3069 to 3349 m) of the NEMO Phase 2 prototype, deployed offshore Capo Passero (Sicily) at the KM3NeT-Italia site, were used to characterize rhythmic bioluminescence patterns in June 2013, in response to water mass movements. We found a significant (p < 0.05) 20.5 h periodicity in the bioluminescence signal, corresponding to inertial fluctuations. Waveform and Fourier analyses of PMT data and tower orientation were carried out to identify phases (i.e. the timing of peaks) by subdividing time series on the length of detected inertial periodicity. A phase overlap between rhythms and cycles suggests a mechanical stimulation of bioluminescence, as organisms carried by currents collide with the telescope infrastructure, resulting in the emission of light. A bathymetric shift in PMT phases indicated that organisms travelled in discontinuous deep-sea undular vortices consisting of chains of inertially pulsating mesoscale cyclones/anticyclones, which to date remain poorly known