The thermodynamics of black holes is investigated in the case of fractal-like event horizon, initially introduced by Barrow. The nature of the horizon surface is controlled by a parameter 0≤Δ≤1 with 0 corresponding to continuous space and 1 to completely fractal one. It is found that the entropy, the Helmholtz free energy, the mass and the heat capacity of the black hole are altered in the presence of non-zero Δ. As the black hole produces Hawking radiation, the dependence of its mass on time becomes softer as Δ increases, resulting in longer evaporation times. This effect makes relatively small primordial black holes to survive long enough so as to be potential ingredients of cold dark matter. The concept of Barrow-type structure can be generalized to the entire space resulting in a modified space-time metric.

Greater interest in long term space travel is creating demand to develop artificial gravity systems that minimize the negative effects of long-term microgravity exposure. However, due to practical constraints of understanding the physiological effects of artificial gravity systems, we propose a cardiovascular simulation to better understand the physiological impacts of an artificial gravity gradient created through the centrifugal force of a rotating spacecraft. The purpose of these simulations is to understand the effects of artificial gravity systems during space travel. We hypothesized that an artificial gravity system will not have significant effects on the cardiovascular system if it induces the same gravity gradient in an upright human as exists on Earth. For this reason, a 10-meter radius, 1 radian/second centrifuge system was chosen to mimic the effect of the gravity gradient on Earth. We used a modified version of the CVSIM program developed to model cardiovascular responses to orthostatic challenges ( https://physionet.org/content/cvsim/1.0.0/ ). CVSIM is a 21-compartment, lumped parameter model with control systems for the cardiopulmonary and arterial baroreflexes. The existing tilt test simulation within the CVSIM program was modified to create a simulation of the centrifuge. A 500-second-long simulation resulted in an average heart rate of 79 beats/minute, an average stroke index of 46 mL/beat/m 2 , and average pressures in the ascending aorta of 99 mmHg during systole, and 72 mmHg during diastole. These values were achieved by 150 seconds into the 500-second simulation. In comparison, prior to the onset of the centrifugation, initial heart rate, stroke index, and ascending aortic pressure compliance were set at 70 beats/min, 46 mL/beat/m 2 , and 0.28 ml/mmHg, respectively, based on published norms in humans. These preliminary data suggests that this artificial gravity system may produce viable physiological conditions for the cardiovascular system. Further research, especially with longer simulations, is necessary to determine if a rotating spacecraft could ease the negative impacts of microgravity over an extended time. This work is supported by Iowa Space Grant Consortium/NASA BASE grant No.103428-19-20 (AP, MJL) This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Many-body correlations in nuclei determine the behavior of Deep-Inelastic-Scattering (DIS) and Quasi-Elastic Scattering (QES) cross section ratios off heavy over light nuclei especially for x Bjorken > 1, obtained at Jefferson Lab.They can be described in terms of quark-cluster formation in nuclei due to wave-function overlapping, manifesting itself when the momentum transfer is high so that the partonic degrees of freedom are resolved.In clusters (correlated nucleons) the quark and gluon momentum distributions are softer than in single nucleons and extend to x Bjorken > 1.The cluster formation probabilities are computed using a network-defining algorithm in which the initial nucleon density is either standard Woods-Saxon or is input from lower energy data while the critical radius for nucleon merging is an adjustable parameter.The exact choice of critical radius depends on the specific nucleus and it is anti-correlated to the rescaling of the x Bjorken needed for bound nucleons.The calculations show that there is a strong dependence of the cross section ratios on the x Bjorken in agreement with the data and that four-body correlations are needed to explain the experimental results even in the range 1

The relativistic Aharonov-Bohm (AB) effect is studied using the time-dependent Dirac equation. It is shown that if the initial electron distribution is a pulse it is possible to define time-dependent signals that distinguish the AB effect from dipole and induced Coulomb interactions.