arXiv subjects
Publications and source records attributed to Nikola Poljak.
We derive the exact expression for the resonant frequency of the time-averaged steady-state energy and show that this frequency is excellently approximated by the arithmetic mean of the amplitude and velocity resonant frequencies. In addition, we argue that the frequency of the amplitude resonance can be regarded as the energy resonance frequency, since it provides the maximal peak values of instantaneous energy.
Theoretically, solutions of the damped harmonic oscillator asymptotically approach equilibrium, i.e., the zero energy state, without ever reaching it exactly, and the critically damped solution approaches equilibrium faster than the underdamped or the overdamped solution. Experimentally, the systems described with this model reach equilibrium when the system's energy has dropped below some threshold corresponding to the energy resolution of the measuring apparatus. We show that one can (almost) always find an optimal underdamped solution that will reach this energy threshold sooner than all other underdamped solutions, as well as the critically damped solution, no matter how small this threshold is. We also comment on one exception to this for a particular type of initial conditions, when a specific overdamped solution reaches the equilibrium state sooner than all other solutions. We confirm some of our findings experimentally.
The properties of decays that take place during jet formation cannot be easily deduced from the final distribution of particles in a detector. In this work, we first simulate a system of particles with well defined masses, decay channels, and decay probabilities. This presents the "true system" for which we want to reproduce the decay probability distributions. Assuming we only have the data that this system produces in the detector, we decided to employ an iterative method which uses a neural network as a classifier between events produced in the detector by the "true system" and some arbitrary "test system". In the end, we compare the distributions obtained with the iterative method to the "true" distributions.
The application of machine learning methods to particle physics often doesn't provide enough understanding of the underlying physics. An interpretable model which provides a way to improve our knowledge of the mechanism governing a physical system directly from the data can be very useful. In this paper, we introduce a simple artificial physical generator based on the Quantum chromodynamical (QCD) fragmentation process. The data simulated from the generator are then passed to a neural network model which we base only on the partial knowledge of the generator. We aim to see if the interpretation of the generated data can provide the probability distributions of basic processes of such a physical system. This way, some of the information we omitted from the network model on purpose is recovered. We believe this approach can be beneficial in the analysis of real QCD processes.
At some point in the future, if mankind hopes to settle planets outside the Solar System, it will be crucial to determine the range of planetary conditions under which human beings could survive and function. In this article, we apply physical considerations to future exoplanetary biology to determine the limitations which gravity imposes on several systems governing the human body. Initially, we examine the ultimate limits at which the human skeleton breaks and muscles become unable to lift the body from the ground. We also produce a new model for the energetic expenditure of walking, by modelling the leg as an inverted pendulum. Both approaches conclude that, with rigorous training, humans could perform normal locomotion at gravity no higher than 4 $g_{\textrm{Earth}}$.
The problem of determining the angle at which a point mass launched from ground level with a given speed is a standard exercise in mechanics. Similar, yet conceptually and calculationally more difficult problems have been suggested to improve student proficiency in projectile motion. The problem of determining the maximum distance of a rock thrown from a rotating arm motion is presented and analyzed in detail in this text. The calculational results confirm several conceptually derived conclusions regarding the initial throw position and provide some details on the angles and the way of throwing (underhand or overhand) which produce the maximum throw distance.
The STAR collaboration has reported precision measurements on the transverse single spin asymmetries for the production of forward $π^0$ mesons from polarized proton collisions at $\sqrt{s} =\,$200 GeV. To disentangle the contributions to forward asymmetries, one has to look beyond inclusive $π^0$ production to the production of forward jets or direct photons. Present forward detector capabilities are not well matched to the complete reconstruction of forward jets, but do have sufficient acceptance for "jet-like" events. "Jet-like" events are the clustered response of an electromagnetic calorimeter that is primarily sensitive to incident photons, electrons and positrons. During the RHIC running in the year 2006, STAR with the Forward Pion Detector (FPD++) in place collected 6.8 pb$^{-1}$ of data with an average polarization of 60%. FPD++ was a modular detector prototype of the Forward Meson Spectrometer (FMS) that consisted of two detectors placed symmetrically with respect to the beam line at a distance of 7.4 m from the interaction point. Readout of the FPD++ was triggered when the sum of energies in the central module of the calorimeter used for $π^0$ measurements was larger than a threshold. This trigger minimizes the bias for "jet-like" events, making it appropriate to disentangling contributions to the forward transverse spin asymmetries. We report on the status of the analysis.
The STAR collaboration has reported precision measurements of the transverse single spin asymmetries for the production of the $π^0$ mesons from polarized proton collisions at $\sqrt{s} = 200$ GeV. These measurements were obtained using modular forward detectors. The Forward Meson Spectrometer (FMS), covering a region of $2.5 < η< 4.0$, and its engineering prototype, provide increased acceptance, as needed for spin-dependent correlation studies that could disentangle contributions to the forward \$pi^0$ asymmetries. We report on the status of the analysis.