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M. Cook

Publications and source records attributed to M. Cook.

16 recordsLinked to original sources
arXiv2026

Incommensurate spin fluctuations in one-dimensional Kondo metal CeCo2Ga8

We present an experimental and numerical study of the spin fluctuations in 1D Kondo metal CeCo$_2$Ga$_8$. Using inelastic neutron spectroscopy, we measure highly one-dimensional magnetism with low-energy incommensurate short-ranged magnetic fluctuations. ARPES similarly shows a highly one-dimensional electronic band structure, confirming the one-dimensional nature of the system. We use density matrix renormalization group (DMRG) simulations of the 1D Kondo lattice model to interpret the measured spectrum, which successfully reproduce the neutron scattering features. We are thus able to place CeCo$_2$Ga$_8$ within the emergent incommensurate phase of the 1D Kondo lattice phase diagram, and demonstrate that the Kondo lattice simulated non-perturbatively is an accurate microscopic model for heavy fermion physics. This shows CeCo$_2$Ga$_8$ to be one-dimensional despite its complexities, and reveals a coexistence of low-energy Kondo and magnetic features in its inelastic spectrum.

cond-mat.str-el↗
arXiv2026

Magnetic Imaging of Macroscopic Spin Chirality Flipping

Chirality is a fundamental organizing principle of correlated and topological states. In quantum magnets, chirality arises from the geometric twisting of spins and serves as an emergent source of Berry curvature and quantum metrics. Although external fields can reversibly tune the spin chirality, understanding how spontaneous reversal occurs on macroscopic length scale remains an unresolved challenge. In this letter, we use resonant magnetic x-ray scattering with 2.5-micron spatial resolution to image intertwined spin, charge, and lattice orders of the correlated topological magnet EuAl4. We uncover a macroscopic chirality flipping transition and a remarkable chiral memory effect. The chiral magnetic domain tracks the landscape of the underlying charge density wave, implicating emergent chiral magnetic interactions arising from competing chiral and nematic lattice fields. Our results reveal the fundamental significance of magnetoelastic coupling in stabilizing homochiral and topological magnetic states.

cond-mat.str-el↗
arXiv2025

Efficient ion re-acceleration in laboratory-produced interpenetrating collisionless shocks

Although the origin of cosmic rays (CRs) remains an open question, collisionless magnetized shock waves are widely regarded as key sites for particle acceleration. Recent theories further suggest that shock-shock collisions in stellar clusters could provide the additional acceleration needed to explain the observed high-energy CR spectrum. Here, we investigate this hypothesis through a laser-based experiment that creates magnetized plasma conditions similar to astrophysical environments. Our results demonstrate that interpenetrating collisionless shocks can significantly boost the energy of ambient protons previously energized by the individual shocks, while also improving the overall acceleration efficiency. Numerical kinetic simulations corroborate these findings, revealing that protons are reaccelerated via their bouncing motion in the convective electric fields of the colliding magnetized flows. By allowing to highly energize ambient protons, our novel colliding-shock platform opens the prospect to test the long-discussed mechanism of diffusive shock acceleration in a controlled laboratory setting.

physics.plasm-ph↗
arXiv2017

Instabilities in Interacting Binary Stars

The types of instability in the interacting binary stars are reviewed. The project "Inter-Longitude Astronomy" is a series of smaller projects on concrete stars or groups of stars. It has no special funds, and is supported from resources and grants of participating organizations, when informal working groups are created. Totally we studied 1900+ variable stars of different types. The characteristic timescale is from seconds to decades and (extrapolating) even more. The monitoring of the first star of our sample AM Her was initiated by Prof. V.P. Tsesevich (1907-1983). Since more than 358 ADS papers were published. Some highlights of our photometric and photo-polarimetric monitoring and mathematical modelling of interacting binary stars of different types are presented: classical, asynchronous, intermediate polars and magnetic dwarf novae (DO Dra) with 25 timescales corresponding to different physical mechanisms and their combinations (part "Polar"); negative and positive superhumpers in nova-like and many dwarf novae stars ("Superhumper"); eclipsing "non-magnetic" cataclysmic variables; symbiotic systems ("Symbiosis"); super-soft sources (SSS, QR And); spotted (and not spotted) eclipsing variables with (and without) evidence for a current mass transfer ("Eclipser") with a special emphasis on systems with a direct impact of the stream into the gainer star's atmosphere, or V361 Lyr-type stars. Other parts of the ILA project are "Stellar Bell" (interesting pulsating variables of different types and periods - M, SR, RV Tau, RR Lyr, Delta Sct) and "Novice"(="New Variable") discoveries and classification with a subsequent monitoring for searching and studying possible multiple components of variability. Special mathematical methods have been developed to create a set of complementary software for statistically optimal modelling of variable stars of different types.

astro-ph.SR↗
arXiv2016

GW Librae: A unique laboratory for pulsations in an accreting white dwarf

Non-radial pulsations have been identified in a number of accreting white dwarfs in cataclysmic variables. These stars offer insight into the excitation of pulsation modes in atmospheres with mixed compositions of hydrogen, helium, and metals, and the response of these modes to changes in the white dwarf temperature. Among all pulsating cataclysmic variable white dwarfs, GW Librae stands out by having a well-established observational record of three independent pulsation modes that disappeared when the white dwarf temperature rose dramatically following its 2007 accretion outburst. Our analysis of HST ultraviolet spectroscopy taken in 2002, 2010 and 2011, showed that pulsations produce variations in the white dwarf effective temperature as predicted by theory. Additionally in May~2013, we obtained new HST/COS ultraviolet observations that displayed unexpected behaviour: besides showing variability at ~275s, which is close to the post-outburst pulsations detected with HST in 2010 and 2011, the white dwarf exhibits high-amplitude variability on a ~4.4h time-scale. We demonstrate that this variability is produced by an increase of the temperature of a region on white dwarf covering up to ~30 per cent of the visible white dwarf surface. We argue against a short-lived accretion episode as the explanation of such heating, and discuss this event in the context of non-radial pulsations on a rapidly rotating star

astro-ph.SR↗
arXiv2011

Modern observations of Hubble's first-discovered Cepheid in M31

We present a modern ephemeris and modern light curve of the first-discovered Cepheid variable in M31, Edwin Hubble's M31-V1. Observers of the American Association of Variable Star Observers undertook these observations during the latter half of 2010. The observations were in support of an outreach program by the Space Telescope Science Institute's Hubble Heritage project, but the resulting data are the first concentrated observations of M31-V1 made in modern times. AAVSO observers obtained 214 V-band, Rc-band, and unfiltered observations from which a current ephemeris was derived. The ephemeris derived from these observations is JD(Max) = 2455430.5(+/-0.5) + 31.4 (+/-0.1) E. The period derived from the 2010 data are in agreement with the historic values of the period, but the single season of data precludes a more precise determination of the period or measurement of the period change using these data alone. However, using an ephemeris based upon the period derived by Baade and Swope we are able to fit all of the observed data acceptably well. Continued observations in the modern era will be very valuable in linking these modern data with data from the 1920s-30s and 1950s, and will enable us to measure period change in this historic Cepheid. In particular, we strongly encourage intensive observations of this star around predicted times of maximum to constrain the date of maximum to better than 0.5 days.

astro-ph.SR↗
arXiv2010

Low-Velocity Impacts on PVDF Targets Using a Light Gas Gun

Orbital debris is a constraint on the long-term health of any spacecraft and must be consi-dered during mission planning. Varying mechanisms have been proposed to quantify the problem. Accurate in-situ data is essential with various types of sensors designed to detect orbital debris impacts employed on space missions since the 1950's [1]. The earliest of these was the PZT (piezoelectric lead zirconate tita-nate) sensor which was often used in-situ to measure the momentum of a particle at the time of impact. More recently, PVDF (Polyvinylidene fluoride) [2] has been employed as it exhibits piezoelectric capabilities along with the advantages of ruggedness, no bias re-quirement, ease of large area sensor construction, high counting rate capability, and space reliability, making it an ideal space debris sensor. Its large sensing sur-face area and ease of integration into a PZT sensor system makes it a desirable element in any in-situ space debris sensor.

physics.space-ph↗
arXiv2009

Two phase galaxy formation: The Gas Content of Normal Galaxies

We investigate the atomic (HI) and molecular (H_2) Hydrogen content of normal galaxies by combining observational studies linking galaxy stellar and gas budgets to their host dark matter (DM) properties, with a physically grounded galaxy formation model. This enables us to analyse empirical relationships between the virial, stellar, and gaseous masses of galaxies and explore their physical origins. Utilising a semi-analytic model (SAM) to study the evolution of baryonic material within evolving DM halos, we study the effects of baryonic infall and various star formation and feedback mechanisms on the properties of formed galaxies using the most up-to-date physical recipes. We find that in order to significantly improve agreement with observations of low-mass galaxies we must suppress the infall of baryonic material and exploit a two-phase interstellar medium (ISM), where the ratio of HI to H_2 is determined by the galactic disk structure. Modifying the standard Schmidt-Kennicutt star formation law, which acts upon the total cold gas in galaxy discs and includes a critical density threshold, and employing a star formation law which correlates with the H_2 gas mass results in a lower overall star formation rate. This in turn, allows us to simultaneously reproduce stellar, HI and H_2 mass functions of normal galaxies.

astro-ph.GA↗
arXiv2009

Two-Phase Galaxy Formation

We propose and test a scenario for the assembly and evolution of luminous matter in galaxies which substantially differs from that adopted by other semianalytic models. As for the dark matter (DM), we follow the detailed evolution of halos within the canonical LCDM cosmology using standard Montecarlo methods. However, when overlaying prescriptions for baryon evolution, we take into account an effect pointed out in the past few years by a number of studies mostly based on intensive N-body simulations, namely that typical halo growth occurs in two phases: an early, fast collapse phase featuring several major merger events, followed by a late, quiescent accretion onto the halo outskirts. We propose that the two modes of halo growth drive two distinct modes for the evolution of baryonic matter, favoring the development of the spheroidal and disc components of galaxies, respectively. We test this idea using the semianalytic technique. Our galaxy formation model envisages an early coevolution of spheroids and the central supermassive black holes, already tested in our previous works, followed by a relatively quiescent growth of discs around the preformed spheroids. In this exploratory study, we couple our model to the spectrophotometric code GRASIL, and compare our results on several properties of the local galaxy population with observations, Finding an encouraging agreement.

astro-ph.GA↗
arXiv2007

Investigation of Dust Wake Field Oscillations

Wakefield oscillations created by the ion wakefield existing below a dust particle within the plasma sheath generated above a powered lower electrode in a GEC rf reference cell carry information about the plasma sheath, the dust particle charge and the speed of the streaming ions. An experimental method to investigate such wakefield oscillations is discussed.

physics.plasm-ph↗
arXiv2006

Low-Velocity Impacts on Targets Containing Embedded Carbon Nanotubes

A one stage Light Gas Gun (LGG) at CASPER [1] was employed to test the shielding capabilities of tiles composed of four different laminated nanotube combinations. These target tiles were named CSNEAT1, CSCNT1, HYCNTUT1 and HYCNTT1. For calibration purposes, a 3003- aluminum plate was also impacted and the craters formed on the various composition tiles compared.

physics.acc-ph↗
arXiv2005

Phase Transitions in a Dusty Plasma with Two Distinct Particle Sizes

In semiconductor manufacturing, contamination due to particulates significantly decreases the yield and quality of device fabrication, therefore increasing the cost of production. Dust particle clouds can be found in almost all plasma processing environments including both plasma etching devices and in plasma deposition processes. Dust particles suspended within such plasmas will acquire an electric charge from collisions with free electrons in the plasma. If the ratio of inter-particle potential energy to the average kinetic energy is sufficient, the particles will form either a liquid structure with short range ordering or a crystalline structure with long range ordering. Otherwise, the dust particle system will remain in a gaseous state. Many experiments have been conducted over the past decade on such colloidal plasmas to discover the character of the systems formed, but more work is needed to fully understand these structures. The preponderance of previous experiments used monodisperse spheres to form complex plasma systems.

astro-ph↗
arXiv2005

Construction of a PZT Sensor Network for Low and Hypervelocity Impact Detection

Orbital debris is a constraint on the long-term health of any spacecraft and must be considered during mission planning. Varying mechanisms have been proposed to quantify the problem. Assessment of orbital debris employing ground-based methods such as radar can help determine where debris clouds are located as well as their density or orbital trajectory. Such data is invaluable to computer simulations and can allow predictions of the debris environment over specific time periods [1]. Accurate in-situ data is essential as well with various types of sensors designed to detect orbital debris impacts employed on space missions since the 1950's [2]. One of the most common of these is the PZT (piezoelectric lead zirconate titanate) which is often used in-situ to measure the momentum of a particle at the time of impact. This paper will discuss a multiple PZT sensor system capable of determining both impactor momentum and location currently in development within CASPER.

physics.space-ph↗
arXiv2003

Dusty Plasma Correlation Function Experiment

Dust particles immersed within a plasma environment, such as those in protostellar clouds, planetary rings or cometary environments, will acquire an electric charge. If the ratio of the inter-particle potential energy to the average kinetic energy is high enough the particles will form either a "liquid" structure with short-range ordering or a crystalline structure with long range ordering. Many experiments have been conducted over the past several years on such colloidal plasmas to discover the nature of the crystals formed, but more work is needed to fully understand these complex colloidal systems. Most previous experiments have employed monodisperse spheres to form Coulomb crystals. However, in nature (as well as in most plasma processing environments) the distribution of particle sizes is more randomized and disperse. This paper reports experiments which were carried out in a GEC rf reference cell modified for use as a dusty plasma system, using varying sizes of particles to determine the manner in which the correlation function depends upon the overall dust grain size distribution. (The correlation function determines the overall crystalline structure of the lattice.) Two dimensional plasma crystals were formed of assorted glass spheres with specific size distributions in an argon plasma. Using various optical techniques, the pair correlation function was determined and compared to those calculated numerically.

physics.space-ph↗
arXiv1997

A smooth surface in P4 not of general type has degree at most 46

This is the continuation of papers by Braun and Floystad, Cook, Braun and Cook. We use Generic Initial Ideal Theory in conjunction with Liaison Theory to further restrict the possible generic initial ideals of hyperplane sections of smooth surfaces not of general type in P4.

alg-geom↗