arXiv subjects

M. Brandt

Publications and source records attributed to M. Brandt.

6 recordsLinked to original sources

arXiv2024

Observation of Critical Scaling in Spin Glasses below Tc using the Thermoremanent Magnetization

Time-dependent Thermoremanent Magnetization (TRM) studies have been instrumental in probing energy dynamics within the spin glass phase. In this paper, we will review the evolution of the TRM experiment over the last half century and discuss some aspects related to how it has been employed in the understanding of spin glasses. We will also report on recent experiments using high resolution DC SQUID magnetometry to probe the TRM at temperatures less than but near to the transition temperature Tc. These experiments have been performed as a function of waiting time, temperature, and five different magnetic fields. We find that as the transition temperature is approached from below, the characteristic time scale of the TRM is suppressed up to several orders of magnitude in time. In the highest temperature region, we find that the waiting time effect goes away, and a waiting time independent crossover line is reached. We also find that increasing the magnetic field, further suppresses the crossover line. Using a first principles energy argument across the crossover line, we derive an equation that is an excellent fit to the crossover lines for all magnetic fields probed. The data show strong evidence for an H = 0 Oe phase transition.

cond-mat.dis-nn↗

arXiv2021

Laboratory Demonstration of the Local Oscillator Concept for the Event Horizon Imager

Black hole imaging challenges the 3rd generation space VLBI, the Very Long Baseline Interferometry, to operate on a 500 GHz band. The coherent integration time needed here is 450 s though the available space oscillators cannot offer more than 10 s. Self-calibration methods might solve this issue in an interferometer formed by 3 antenna/satellite systems, but the need for the 3rd satellite increases mission costs. A frequency transfer is of special interest to alleviate both performance and cost issues. A concept of 2-way optical frequency transfer is examined to investigate its suitability to enable space-to-space interferometry, in particular, to image the 'shadows' of black holes from space. The concept, promising on paper, has been demonstrated by tests. The laboratory test set-up is presented and the verification of the temporal stability using standard analysis tool as TimePod has been passed. The resulting Allan Deviation is dominated by the 1/$τ$ phase noise trend since the frequency transfer timescale of interest is shorter than 0.2 s. This trend continues into longer integration times, as proven by the longest tests spanning over a few hours. The Allan Deviation between derived 103.2 GHz oscillators is $1.1\times10^{-14}/τ$ within 10 ms < $τ$ < 1,000 s that degrades twice towards the longest delay 0.2 s. The worst case satisfies the requirement with a margin of 11 times. The obtained coherence in the range of 0.997-0.9998 is beneficial for space VLBI at 557 GHz. The result is of special interest to future science missions for black hole imaging from space.

astro-ph.IM↗

arXiv2020

Grain refinement of stainless steel in ultrasound-assisted additive manufacturing

Metals and alloys fabricated by fusion-based additive manufacturing (AM), or 3D printing, undergo complex dynamics of melting and solidification, presenting challenges to the effective control of grain structure. Herein, we report on the use of high-intensity ultrasound that controls the process of solidification during AM of 316L stainless steel. We find that the use of ultrasound favours the columnar-to-equiaxed transition, promoting the formation of fine equiaxed grains with random crystallographic texture. Moreover, the use of ultrasound increases the number density of grains from 305 mm-2 to 2748 mm-2 despite an associated decrease in cooling rate and temperature gradient in the melt pool during AM. Our assessment of the relationship between grain size and cooling rate indicates that the formation of crystallites during AM is enhanced by ultrasound. Furthermore, the use of ultrasound increases the amount of constitutional supercooling during solidification by lowering the temperature gradient in the bulk of the melt pool, thus creating an environment that favours nucleation, growth, and survival of grains. This new understanding provides opportunities to better exploit ultrasound to control grain structure in AM-fabricated metal products.

physics.app-ph↗

arXiv2015

Squeezing of quantum noise of motion in a micromechanical resonator

A pair of conjugate observables, such as the quadrature amplitudes of harmonic motion, have fundamental fluctuations which are bound by the Heisenberg uncertainty relation. However, in a squeezed quantum state, fluctuations of a quantity can be reduced below the standard quantum limit, at the cost of increased fluctuations of the conjugate variable. Here we prepare a nearly macroscopic moving body, realized as a micromechanical resonator, in a squeezed quantum state. We obtain squeezing of one quadrature amplitude $1.1 \pm 0.4$ dB below the standard quantum limit, thus achieving a long-standing goal of obtaining motional squeezing in a macroscopic object.

cond-mat.mes-hall↗

arXiv2014

Nuclear parton density modifications from low-mass lepton pair production at the LHC

In this article, we investigate the potential of low-mass lepton pair production in proton-ion collisions at the LHC to constrain nuclear modifications of parton densities. Similarly to prompt photon production, the transverse momentum spectrum is shown to be dominated by the QCD Compton process, but has virtually no fragmentation or isolation uncertainties. Depending on the orientation of the proton and ion beams and on the use of central or forward detector components, all interesting regions of nuclear effects (shadowing, antishadowing, isospin and EMC effects) can be probed. Ratios of cross sections allow to eliminate theoretical scale and bare-proton parton density errors as well as many experimental systematic uncertainties.

hep-ph↗

arXiv2013

Parton densities from LHC vector boson production at small and large transverse momenta

The parton densities of the proton are of fundamental importance not only for our description of hadronic and nuclear structure, but also for reliable predictions for new heavy particle searches at colliders. At the large partonic momentum fractions required for the production of these particles, the parton distribution functions, in particular the one of the gluon, are unfortunately still badly constrained. In this paper, we investigate the possibility to improve on their determination with new data coming from electroweak vector boson production at large transverse momenta at the LHC with center-of-mass energies of 7, 8 or 14 TeV. We demonstrate that this process is dominated by quark-gluon scattering, that theoretical predictions can be reliably made on the basis of next-to-leading order perturbation theory and its resummation, and that these data should thus be used in global fits. We also point out that the non-perturbative parameters determined from Tevatron run-1 Z-boson data at low p_T describe very well the new LHC data at \sqrt{s}=7 TeV.

hep-ph↗