Exponential versus linear amplitude decay in damped oscillators

We comment of the widespread belief among some undergraduate students that the amplitude of any harmonic oscillator in the presence of any type of friction, decays exponentially in time. To dispel that notion, we compare the amplitude decay for a harmonic oscillator in the presence of (i) viscous friction and (ii) dry friction. It is shown that, in the first case, the amplitude decays exponentially with time while in the second case, it decays linearly with time.Comment: 3 pages, 1 figure, accepted in Phys. Teac

The Transformation of Jewish Mysticism in Mikhail Bulgakov’s The White Guard

The article was submitted on 02.02.2015.Анализируются элементы еврейской мистики, к которым обращается Михаил Булгаков в романе «Белая гвардия». Ставится задача проследить источники мотивов, служащих для создания мифологического антуража в романе. Автором выявлено многократное использование элементов еврейской мистики в обрисовке образов. Михаил Шполянский, является собирательным образом «нечистой» силы и одновременно несет в себе семантику Мессии. По еврейским представлениям, Мессия должен страдать от отвратительных, открытых, гноящихся ран. Пациент Шполянский также страдает отталкивающей болезнью, но его недуги скрыты от людей, в отличие недугов еврейского Мессии. Отвращение, вызываемое ранами Мессии, предназначено для испытания степени человеколюбия и милосердия людей, во имя которых он должен сойти в этот мир. Если еврей сумеет преодолеть свое отвращение к ранам Мессии и поможет ему, проявив великодушие и сострадание, - тогда Бог излечит мнимые недуги Мессии и пошлет его к людям, где он установит Свое царство и освободит мир от всеобщего страдания. Автор ставит проблему, насколько осознанно обращался писатель к еврейским источникам, трактующим болезни Мессии и показывающим их в излишне натурализированном описании? Выявляется отход Булгакова от традиционной еврейской трактовки Аваддона, используемого писателем для обозначения Антихриста, который символизирует Демона Тьмы и Разрушения. Элементы из древнееврейских источников, которые широко использует Булгаков при описании потустороннего, мистического и демонического, фигурируют в несвойственном еврейскому оригиналу значении, что, вероятно, обусловлено тем, что Булгаков использовал сведения о еврейской мифологии, почерпнутые из Энциклопедического словаря Брокгауза и Ефрона. Но в этом издании еврейская мифология представлена в не соответствующих оригиналу характеристиках. Однако эти неточности не умаляют того факта, что Булгакову удалось создать в романе атмосферу, пропитанную древними еврейскими мистическими представлениями, и убедить в этом читателя.The article analyzes the elements of Jewish mysticism employed by Mikhail Bulgakov in his The White Guard and aims to trace the sources of motifs used to create a sense of mystery in the novel. The author enumerates multiple uses of Jewish mystical elements in the depiction of the characters. Mikhail Shpolyansky is both an image of the evil and refers to the Messiah. According to Jewish beliefs, the Messiah must suffer from disgusting open fester wounds. Likewise, Shpolyansky suffers from a repugnant disease but his ailment is unknown to the public unlike that of the Jewish Messiah. The disgust caused by the Messiah’s wounds is meant to verify the scale of humaneness and the capacity for mercy in the ones for whose sake the Messiah must descend to this world. If Jews can overcome the disgust they feel when looking at the Messiah’s wounds and help him, demonstrating benevolence and compassion, God will heal the Messiah’s imaginary diseases and send him to people where he will rule in God’s name and usher in a time of peace and eliminate all suffering. The author questions whether the use of Jewish sources was a conscious decision made by Bulgakov, when he interpreted the Messiah’s diseases and gave gory details of them. The question is that if Bulgakov emphasizes disgust caused by the patient and by his demonic nature, why he did not consider the motif of the repugnant wounds of the Jewish Messiah then. The author describes the writer’s digression from the traditional Jewish interpretation of Abaddon used by Bulgakov to refer to Antichrist who symbolizes the Demon of Darkness and Destruction. The elements of Old Jewish sources extensively used by Bulgakov when describing the supernatural, mystical and demonic quite often possess a meaning uncharacteristic of the one used in the Jewish original and are quite often presented inaccurately. It is likely to have been caused by the fact that while creating the mystical background of the novel, Bulgakov relied on the data on Jewish mythology he could find in the Brockhaus and Efron Encyclopedic Dictionary. However, it does not reflect the original meaning of Jewish mythology but gives a distorted picture of it. Despite the discrepancies, Bulgakov managed to create an atmosphere filled with Old Jewish mystical beliefs and do it convincingly for the reader

On the Gerasimov-Drell-Hearn sum rule for the deuteron

The Gerasimov-Drell-Hearn sum rule is evaluated for the deuteron by explicit integration up to 550 MeV including contributions from the photodisintegration channel and from coherent and incoherent single pion production as well. The photodisintegration channel converges fast enough in this energy range and gives a large negative contribution, essentially from the $^1S_0$ resonant state near threshold. Its absolute value is about the same size as the sum of proton and neutron GDH values. It is only partially cancelled by the single pion production contribution. But the incoherent channel has not reached convergence at 550 MeV.Comment: 6 pages latex including 3 postscript figures, talk at the 15th Int. Conf. on Few-Body Problems in Physics, Groningen, Netherlands, 22-26 July 1997. To be published in Nucl. Phys.

Avaliação da severidade da murcha de fusário em tomateiro em diferentes níveis de água no solo por meio da temperatura na superficie foliar.

O objetivo do trabalho foi avaliar o efeito do manejo de água de irrigação por meio de diferentes níveis de água no solo sobre o desenvolvimento temporal da murcha de fusário em tomateiro.Resumo 849-1

Q^2 Evolution of Generalized Baldin Sum Rule for the Proton

The generalized Baldin sum rule for virtual photon scattering, the unpolarized analogy of the generalized Gerasimov-Drell-Hearn integral, provides an important way to investigate the transition between perturbative QCD and hadronic descriptions of nucleon structure. This sum rule requires integration of the nucleon structure function F_1, which until recently had not been measured at low Q^2 and large x, i.e. in the nucleon resonance region. This work uses new data from inclusive electron-proton scattering in the resonance region obtained at Jefferson Lab, in combination with SLAC deep inelastic scattering data, to present first precision measurements of the generalized Baldin integral for the proton in the Q^2 range of 0.3 to 4.0 GeV^2.Comment: 4 pages, 3 figures, one table; text added, one figure replace

Analysis of ultrasonic transducers with fractal architecture

Ultrasonic transducers composed of a periodic piezoelectric composite are generally accepted as the design of choice in many applications. Their architecture is normally very regular and this is due to manufacturing constraints rather than performance optimisation. Many of these manufacturing restrictions no longer hold due to new production methods such as computer controlled, laser cutting, and so there is now freedom to investigate new types of geometry. In this paper, the plane wave expansion model is utilised to investigate the behaviour of a transducer with a self-similar architecture. The Cantor set is utilised to design a 2-2 conguration, and a 1-3 conguration is investigated with a Sierpinski Carpet geometry

Sum Rules for Magnetic Moments and Polarizabilities in QED and Chiral Effective-Field Theory

We elaborate on a recently proposed extension of the Gerasimov-Drell-Hearn (GDH) sum rule which is achieved by taking derivatives with respect to the anomalous magnetic moment. The new sum rule features a {\it linear} relation between the anomalous magnetic moment and the dispersion integral over a cross-section quantity. We find some analogy of the linearized form of the GDH sum rule with the `sideways dispersion relations'. As an example, we apply the linear sum rule to reproduce the famous Schwinger's correction to the magnetic moment in QED from a tree-level cross-section calculation and outline the procedure for computing the two-loop correction from a one-loop cross-section calculation. The polarizabilities of the electron in QED are considered as well by using the other forward-Compton-scattering sum rules. We also employ the sum rules to study the magnetic moment and polarizabilities of the nucleon in a relativistic chiral EFT framework. In particular we investigate the chiral extrapolation of these quantities.Comment: 24 pages, 7 figures; several additions, published versio

Importance of Compton scattering to radiation spectra of isolated neutron stars

Model atmospheres of isolated neutron stars with low magnetic field are calculated with Compton scattering taking into account. Models with effective temperatures 1, 3 and 5 MK, with two values of surface gravity log(g)g = 13.9 and 14.3), and different chemical compositions are calculated. Radiation spectra computed with Compton scattering are softer than the computed with Thomson scattering at high energies (E > 5 keV) for hot (T_eff > 1 MK) atmospheres with hydrogen-helium composition. Compton scattering is more significant to hydrogen models with low surface gravity. The emergent spectra of the hottest (T_eff > 3 MK) model atmospheres can be described by diluted blackbody spectra with hardness factors ~ 1.6 - 1.9. Compton scattering is less important for models with solar abundance of heavy elements.Comment: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.173-17

Z2_2 topology and superconductivity from symmetry lowering of a 3D Dirac Metal Au2_2Pb

3D Dirac semi-metals (DSMs) are materials that have massless Dirac electrons and exhibit exotic physical properties It has been suggested that structurally distorting a DSM can create a Topological Insulator (TI), but this has not yet been experimentally verified. Furthermore, quasiparticle excitations known as Majorana Fermions have been theoretically proposed to exist in materials that exhibit superconductivity and topological surface states. Here we show that the cubic Laves phase Au$_2$Pb has a bulk Dirac cone above 100 K that gaps out upon cooling at a structural phase transition to create a topologically non trivial phase that superconducts below 1.2 K. The nontrivial Z$_2$ = -1 invariant in the low temperature phase indicates that Au$_2$Pb in its superconducting state must have topological surface states. These characteristics make Au$_2$Pb a unique platform for studying the transition between bulk Dirac electrons and topological surface states as well as studying the interaction of superconductivity with topological surface states

Conformational spread as a mechanism for cooperativity in the bacterial flagellar switch

The bacterial flagellar switch that controls the direction of flagellar rotation during chemotaxis has a highly cooperative response. This has previously been understood in terms of the classic two-state, concerted model of allosteric regulation. Here, we used high-resolution optical microscopy to observe switching of single motors and uncover the stochastic multistate nature of the switch. Our observations are in detailed quantitative agreement with a recent general model of allosteric cooperativity that exhibits conformational spread—the stochastic growth and shrinkage of domains of adjacent subunits sharing a particular conformational state. We expect that conformational spread will be important in explaining cooperativity in other large signaling complexes