On the Question of the Source of the Apokamp

Technical Physics - The object of this work is the apokamp—a new type of plasma jet, which is formed from a bright offshoot emerging at the bending point of a channel of a high-voltage...     

Set the controls for the heart of the Sun

In this paper we describe experiments conducted with high-power lasers that are attempting to replicate, for a very short time and in miniature, conditions found in the Sun. Experiments to date have reached conditions in the outer part of the Sun. To reach the Sun's centre requires compression of material to very much greater than solid density and heating to over ten million degrees. To achieve this, a new class of experiments and a new generation of high-power lasers are required.     

On the Possibility of the Implicit Renormalization of the Casimir Energy

We propose a procedure for renormalizing the Casimir energy that makes the steps that are used in the standard renormalization procedure, that is, regularization, subtraction, and deregularization, implicit. The proposed procedure is based on the calculation of a set of convergent sums, each of which is related to the initial divergent sum of the non-renormalized Casimir energy. Next, we construct a system of linear equations that relates this set of convergent sums to the renormalized Casimir energy. The unknown renormalized Casimir energy is obtained as a result of solving this system of equations. In this case, both the calculations of the convergent sums and the subsequent solution of the system of linear equations are performed with a certain (generally speaking, arbitrary) ordered accuracy; thus, the result is also approximate. The proposed procedure is, first, more computationally effective than the standard one, and, second, applicable not only to the problems where a transcendental equation for the spectrum can be written, but also to the problems where the spectrum is known only numerically.     

Violations of the Pauli principle and the interior of the sun

The consequences of a violation of the Pauli principle for the physics of the solar interior are explored. It is found that a bound state of two protons becomes possible. This leads to an increase in the rate of hydrogen burning in the sun. Because a very large cross section for this reaction is in clear contradiction with the theory of stellar structure when compared with observations of solar luminosity, radius and mechanical oscillations, stringent limits on a violation of the Pauli principle in the two nucleon system can be given. However, a very small violation of the Pauli principle in the two nucléon system might solve the longstanding solar neutrino problem.     

Contributions of the cornea and the lens to the aberrations of the human eye

The relative contributions of optical aberrations of the cornea and the crystalline lens to the final image quality of the human eye were studied. The aberrations of the entire eye were obtained from pairs of double-pass retinal images, and the aberrations of the cornea were obtained from videokeratographic data. Third-order spherical aberration and coma were significantly larger for the cornea than for the complete eye, indicating a significant role of the lens in compensating for corneal aberrations. In a second experiment retinal images were recorded in an eye before and after we neutralized the aberrations of the cornea by having the subjects wear swimming goggles filled with saline water, providing a direct estimate of the optical performance of the crystalline lens.     

On the calculation of the bremsstrahlung in the region of the plasma frequency

On the basis of the classical theory of radiation produced in incomplete Coulomb interaction, a formula is derived for the coefficient of the bremsstrahlung of fully ionized plasma. In the region of rectilinear approximation a comparison is made with the results of the quantum formula derived from the Born approximation. Furthermore, the influence of dispersion upon the emission coefficient is taken into account; some relations for the region of dispersion are given.     

Probing the structure of the pomeron

We suggest that the pseudo-rapidity cut dependence of diffractive deep-inelastic scattering events at HERA may provide a sensitive test of models of diffraction. A comparison with the experimental cross section shows that the Donnachie-Landshoff model and a simple two-gluon exchange model of the pomeron model are disfavoured. However a model with a direct coupling of the pomeron to quarks is viable for a harder quark–pomeron form factor, as is a model based on the leading-twist operator contribution. We also consider a direct-coupling scalar pomeron model. We comment on the implications of these results for the determination of the partonic structure of the pomeron. Received: 5 March 1999 / Published online: 3 August 1999     

Confronting the MSSM and the NMSSM with the discovery of a signal in the two photon channel at the LHC

We confront the discovery of a boson decaying into two photons, as reported recently by ATLAS and CMS, with the corresponding predictions in the Minimal Supersymmetric Standard Model (MSSM) and the Next-to-Minimal Supersymmetric Standard Model (NMSSM). We perform a scan over the relevant regions of parameter space in both models and evaluate the MSSM and NMSSM predictions for the dominant Higgs production channel and the photon–photon decay channel. Taking into account the experimental constraints from previous direct searches, flavor physics, electroweak measurements as well as theoretical considerations, we find that a Higgs signal in the two photon channel with a rate equal to, or above, the SM prediction is viable over the full mass range 123?M _H ?127 GeV, both in the MSSM and the NMSSM. We find that besides the interpretation of a possible signal at about 125 GeV in terms of the lightest $\mathcal {CP}$ -even Higgs boson, both the MSSM and the NMSSM permit also a viable interpretation where an observed state at about 125 GeV would correspond to the second-lightest $\mathcal {CP}$ -even Higgs boson in the spectrum, which would be accompanied by another light Higgs with suppressed couplings to W and Z bosons. We find that a significant enhancement of the γγ rate, compatible with the signal strengths observed by ATLAS and CMS, is possible in both the MSSM and the NMSSM, and we analyse in detail different mechanisms in the two models that can give rise to such an enhancement. We briefly discuss also our predictions in the two models for the production and subsequent decay into two photons of a $\mathcal {CP}$ -odd Higgs boson.     

On the possibility to optimize the gain of the Compton laser

The gain of the Compton laser is derived in the case when the direction of propagation of the amplified wave does not coincide with the direction of motion of an electron beam. The optimum geometry of the experiment is found. Numerical estimations are presented, which show that there is a possibility to achieve a noticeable amplification in the ultra-violet region using a CO₂ laser as a pump.     

Distinguishing the higgs boson from the dilaton at the large hadron collider

It is likely that the LHC will observe a color- and charge-neutral scalar whose decays are consistent with those of the standard model (SM) Higgs boson. The Higgs interpretation of such a discovery is not the only possibility. For example, electroweak symmetry breaking could be triggered by a spontaneously broken, nearly conformal sector. The spectrum of states at the electroweak scale would then contain a narrow scalar resonance, the pseudo-Goldstone boson of conformal symmetry breaking, with Higgs-boson-like properties. If the conformal sector is strongly coupled, this pseudodilaton may be the only new state accessible at high energy colliders. We discuss the prospects for distinguishing this mode from a minimal Higgs boson at the LHC and ILC. The main discriminants between the two scenarios are (i) cubic self-interactions and (ii) a potential enhancement of couplings to massless SM gauge bosons.     

Application of the structured illumination method to study the topography of the sole of the foot during a walk

The structured illumination technique consists of projecting a fringe system onto a 3D object from a well defined space point, which results in a pattern that depends on the characteristic of the projected fringes, the viewpoint and the illuminated object morphology. Therefore, the structured illumination method enables to determine the topography of 3D objects. To implement this technique we set up an optoelectronic array that allows studying the sole of the foot during a walk. The method consists of projecting a Ronchi grid and capturing the images generated on the foot by a CCD camera. These obtained images are graphically processed and fringes converted into vectors. A depending algorithm on the experimental setup allows obtaining, from those vectors data, cotes for a discrete profile plotting of the studied object. The method enables the quantitative determination of the sole topography during the walk. Qualitatively, it can be used for diagnosis and control of deformation and injuries caused by accidents or illnesses. It can be introduced in the primary attention health system to study a great number of patients, due to its simplicity and low cost installation, and for being a non-invasive technique.     

On the numerical solution of the biharmonic equation in the plane

The biharmonic equation arises in a variety of problems in applied mathematics, most notably in plane elasticity and in viscous incompressible flow. Integral equation methods are natural candidates for the numerical solution of such problems, since they discritize the boundary alone, are easy to apply in the case of free or moving boundaries, and achieve superalgebraic convergence rates on sufficiently smooth domains, regardless of shape. In this paper, we follow the work of Mayo and Greenbaum and make use of the Sherman-Lauricella integral equation which is a Fredholm equation with bounded kernel. We describe a fast algorithm for the evaluation of the integral operators appearing in that equation. When combined with a conjugate gradient like algorithm, we are able to solve the discretized integral equation in an amount of time proportional to N, where N is the number of nodes in the discretization of the boundary.     

Influence of the thickness of the liquid layer on the ratio of the dimensions of a convection cell

A theory is developed for a new type of transition — a change in the ratio of the longitudinal and transverse dimensions of a convection cell as the thickness of a liquid layer is varied. A sudden change in the ratio of the cell dimensions takes place because of a change in the predominant mechanism for excitation of convection. The governing influence of buoyancy forces gives way to one of thermocapillary forces, and they in turn give way to the influence of thermoelectric forces for yet thinner layers. As the layer thickness is reduced gradually at a fixed external heating, the ratio of the dimensions will take on the values 0.7, 0.65, and 1, respectively. Zh. Tekh. Fiz. 68, 7–11 (November 1998)     

Remarks concerning the derivation and the expansion of the master equation

The present work consist of two parts: In the first part we apply the method of quasilinearization to the differential equation describing the time development of the quantum-mechanical probability density. In this way we derive the master equation without resorting to perturbation theory. In the second part of the paper, for a general form of the master equation which is an integro-differential equation, we test the accuracy of the Fokker-Planck approximation with the help of a solvable model. Then we study an alternative way of reducing the integro-differential equation to a partial differential equation. By expanding the transition probability W(q, q′), and the distribution function in terms of a complete set of functions, we show that for certain forms of W(q, q′), the master equation can be transformed exactly to partial differential equations of finite order.     

On the NLO QCD corrections to the production of the heaviest neutral Higgs scalar in the MSSM

We present a calculation of the two-loop top–stop–gluino contributions to Higgs production via gluon fusion in the MSSM. By means of an asymptotic expansion in the heavy particle masses, we obtain explicit and compact analytic formulas that are valid when the Higgs and the top quark are lighter than stops and gluino, without assuming a specific hierarchy between the Higgs mass and the top mass. Being applicable to the heaviest Higgs scalar in a significant region of the MSSM parameter space, our results complement earlier ones obtained with a Taylor expansion in the Higgs mass, and can be easily implemented in computer codes to provide an efficient and accurate determination of the Higgs production cross section.     

Status of the energy-buncher in the low-energy branch of the Super-FRS

An ion-optical study on the layout of the so-called energy-buncher stage in the low-energy branch of the planned fragment separator Super-FRS is presented. The main purpose of the energy-buncher is a significant reduction of the energy spread of the `hot' fragments at the exit of the separator. Alternatively, the central unit of the buncher—a large dispersive dipole system—can be used as a high-resolution spectrometer for secondary products of nuclear reactions. The proposed design provides a large degree of flexibility for different experimental scenarios with slowed-down low-energy or stopped exotic isotopes.     

On the theory of the Buckingham effect

We apply general arguments (based on spatial transformation properties, intrinsic symmetry and dimensional analysis) to the theory of the Buckingham effect (electric-field–gradient-induced birefringence in a gas). These yield, in a simple manner, the temperature-dependent and temperature-independent terms in the birefringence (each to within a numerical factor), and also the expression, derived by Buckingham and Longuet-Higgins, for the effective quadrupole centre of a molecule. We show in addition how the calculation of the two numerical factors can be simplified in our approach.     

Testing the mechanism for the LSP stability at the LHC

The lightest supersymmetric particle (LSP) is a natural candidate for the cold dark matter of the universe. In this Letter we discuss how to test the mechanism responsible for the LSP stability at the LHC. We note that if R-parity is conserved dynamically one should expect a Higgs boson which decays mainly into two right-handed neutrinos (a “leptonic” Higgs) or into two sfermions. The first case could exhibit spectacular lepton number violating signals with four secondary vertices due to the long-lived nature of right-handed neutrinos. These signals, together with the standard channels for the discovery of SUSY, could help to establish the underlying theory at the TeV scale.     

Adam and the Ants: On the Influence of the Optimization Algorithm on the Detectability of DNN Watermarks

As training Deep Neural Networks (DNNs) becomes more expensive, the interest in protecting the ownership of the models with watermarking techniques increases. Uchida et al. proposed a digital watermarking algorithm that embeds the secret message into the model coefficients. However, despite its appeal, in this paper, we show that its efficacy can be compromised by the optimization algorithm being used. In particular, we found through a theoretical analysis that, as opposed to Stochastic Gradient Descent (SGD), the update direction given by Adam optimization strongly depends on the sign of a combination of columns of the projection matrix used for watermarking. Consequently, as observed in the empirical results, this makes the coefficients move in unison giving rise to heavily spiked weight distributions that can be easily detected by adversaries. As a way to solve this problem, we propose a new method called Block-Orthonormal Projections (BOP) that allows one to combine watermarking with Adam optimization with a minor impact on the detectability of the watermark and an increased robustness.