arXiv subjects

Javier Garcia

Publications and source records attributed to Javier Garcia.

At least 19 recordsLinked to original sources

arXiv2025

Moving Matter: Using a Single, Simple Robot to Reconfigure a Connected Set of Building Blocks

We implement and evaluate different methods for the reconfiguration of a connected arrangement of tiles into a desired target shape, using a single active robot that can move along the tile structure. This robot can pick up, carry, or drop off one tile at a time, but it must maintain a single connected configuration at all times. Becker et al. (CCCG 2025) recently proposed an algorithm that uses histograms as canonical intermediate configurations, guaranteeing performance within a constant factor of the optimal solution if the start and target configuration are well-separated. We implement and evaluate this algorithm, both in a simulated and practical setting, using an inchworm type robot to compare it with two existing heuristic algorithms.

cs.RO↗

arXiv2025

XRISM Spectroscopy of the Stellar-Mass Black Hole 4U 1630-472 in Outburst

We report on XRISM/Resolve spectroscopy of the recurrent transient and well-known black hole candidate 4U 1630$-$472 during its 2024 outburst. The source was captured at the end of a disk-dominated high/soft state, at an Eddington fraction of $\lambda_\mathrm{Edd} \sim 0.05~(10 M_{\odot}/M_\mathrm{BH})$. A variable absorption spectrum with unprecedented complexity is revealed with the Resolve calorimeter. This marks one of the lowest Eddington fractions at which highly ionized absorption has been detected in an X-ray binary. The strongest lines are fully resolved, with He-like Fe XXV separated into resonance and intercombination components, and H-like Fe XXVI seen as a spin-orbit doublet. The depth of some absorption lines varied by almost an order of magnitude, far more than expected based on a 10% variation in apparent X-ray flux and ionization parameter. The velocity of some absorption components also changed significantly. Jointly modeling two flux segments with a consistent model including four photoionization zones, the spectrum can be described in terms of highly ionized but likely failed winds that sometimes show red-shifts, variable obscuration that may signal asymmetric structures in the middle and outer accretion disk, and a tentative very fast outflow ($v = 0.026-0.033c$). We discuss the impact of these findings on our understanding of accretion and winds in stellar-mass black holes, and potential consequences for future studies.

astro-ph.HE↗

arXiv2025

Hybrid Team Tetris: A New Platform For Hybrid Multi-Agent, Multi-Human Teaming

Metcalfe et al (1) argue that the greatest potential for human-AI partnerships lies in their application to highly complex problem spaces. Herein, we discuss three different forms of hybrid team intelligence and posit that across all three forms, the hybridization of man and machine intelligence can be effective under the right conditions. We foresee two significant research and development (R&D) challenges underlying the creation of effective hybrid intelligence. First, rapid advances in machine intelligence and/or fundamental changes in human behaviors or capabilities over time can outpace R&D. Second, the future conditions under which hybrid intelligence will operate are unknown, but unlikely to be the same as the conditions of today. Overcoming both of these challenges requires a deep understanding of multiple human-centric and machine-centric disciplines that creates a large barrier to entry into the field. Herein, we outline an open, shareable research platform that creates a form of hybrid team intelligence that functions under representative future conditions. The intent for the platform is to facilitate new forms of hybrid intelligence research allowing individuals with human-centric or machine-centric backgrounds to rapidly enter the field and initiate research. Our hope is that through open, community research on the platform, state-of-the-art advances in human and machine intelligence can quickly be communicated across what are currently different R&D communities and allow hybrid team intelligence research to stay at the forefront of scientific advancement.

cs.HC↗

arXiv2025

Cepstrum-based interferometric microscopy (CIM) for quantitative phase imaging

A universal methodology for coding-decoding the complex amplitude field of an imaged sample in coherent microscopy is presented, where no restrictions on any of the two interferometric beams are required. Thus, the imaging beam can be overlapped with, in general, any other complex amplitude distribution and, in particular, with a coherent and shifted version of itself considering two orthogonal directions. The complex field values are retrieved by a novel Cepstrum-based algorithm, named as Spatial-Shifting Cepstrum (SSC), based on a weighted subtraction of the Cepstrum transform in the cross-correlation term of the object field spectrum in addition with the generation of a complex pupil from the combination of the information retrieved from different holographic recordings (one in horizontal and one in vertical direction) where one of the interferometric beams is shifted 1 pixel. As a result, the field of view is tripled since the complex amplitudes of the three interferometric fields involved in the process are retrieved. Proof-of-concept validation of this methodology, named as Cepstrum-based Interferometric Microscopy (CIM), is provided considering an off-axis holographic configuration for retrieving the cross-correlation of the two interferometric complex amplitude fields in a compact quasi-common path Michelson interferometric configuration. Experimental results for different types of phase samples (resolution test targets for step-by-step calibration and demonstration as well as fixed biosamples) are included.

physics.optics↗

arXiv2025

Spatially Multiplexed Interferometric Microscopy with one-dimensional diffraction grating

Digital holographic microscopy (DHM) applied to quantitative phase imaging (QPI) has been successfully demonstrated as a powerful label-free method to analyse the optical properties of cells. Spatially multiplexed interferometric microscopy (SMIM) is a DHM technique that implements a common-path interferometric layout in the embodiment of a standard microscope to achieve QPI. More concretely, SMIM introduces three minimal modifications: 1) replaces the broadband illumination of the microscope by a coherent or partially coherent light source, 2) divides the input plane into two or three regions for transmission in parallel of both imaging and reference beams, and 3) includes a one-dimensional diffraction grating or a beam splitter cube for holographic recording. Hence, SMIM is a cost-effective, extremely simple, and highly stable manner of converting a standard bright field microscope into a holographic one. The goal of this contribution is to provide a review of the SMIM approaches implemented using a one-dimensional (1D) diffraction grating, and highlight vast range of capabilities including super-resolved, reflective, transflective, noise-reduced and single-shot slightly off-axis amplitude and phase imaging.

physics.optics↗

arXiv2025

Resolution enhancement in quantitative phase microscopy: a review

Quantitative phase microscopy (QPM), a technique combining phase imaging and microscopy, enables visualization of the 3D topography in reflective samples, as well as the inner structure or refractive index distribution of transparent and translucent samples. Similar to other imaging modalities, QPM is constrained by the conflict between numerical aperture (NA) and field of view (FOV): an imaging system with a low NA has to be employed to maintain a large FOV. This fact severely limits the resolution in QPM up to being the illumination wavelength. Consequently, finer structures of samples cannot be resolved by using modest NA objectives in QPM. Aimed to that, many approaches, such as oblique illumination, structured illumination, and speckle illumination (just to cite a few), have been proposed to improve the spatial resolution (or the space bandwidth product) in phase microscopy by restricting other degrees of freedom (mostly time). This paper aims to provide an up to date review on the resolution enhancement approaches in QPM, discussing the pros and cons of each technique as well as the confusion on resolution definition claims on QPM and other coherent microscopy methods. Through this survey, we will review the most appealing and useful techniques for superresolution in coherent microscopy, working with and without lenses and with special attention to QPM.

physics.optics↗

arXiv2025

Variable zoom digital in-line holographic microscopy

We report on a novel layout providing variable zoom in digital in-line holographic microscopy (VZ-DIHM). The implementation is in virtue of an electrically tunable lens (ETL) which enables to slightly shift the illumination source axial position without mechanical movement of any system component. Magnifications ranging from 15X to 35X are easily achievable using the same layout and resulting in a substantial variation of the total field of view (FOV). The performance of the proposed setup is, first, validated using a resolution test target where the main parameters are analyzed (theoretically and experimentally) and, second, corroborated analyzing biological sample (prostate cancer cells) showing its application to biomedical imaging.

physics.optics↗

arXiv2025

Fluholoscopy. Compact and Simple Platform Combining Fluorescence and Holographic Microscopy

The combination of different imaging modalities into single imaging platforms has a strong potential in biomedical sciences since it permits the analysis of complementary properties of the target sample. Here, we report on an extremely simple, cost-effective, and compact microscope platform for achieving simultaneous fluorescence and quantitative phase imaging modes with the capability of working in a single snapshot. It is based on the use of a single illumination wavelength to both excite the sample fluorescence and provide coherent illumination for phase imaging. After passing the microscope layout, the two imaging paths are separated by using a bandpass filter and the two imaging modes are simultaneously obtained by using two digital cameras. We first present calibration and analysis of both fluorescence and phase imaging modalities working independently and, later on, experimental validation for the proposed common-path dual-mode imaging platform considering static (resolution test targets, fluorescent micro-beads and water-suspended lab-made cultures) as well as dynamic (flowing fluorescent beads, human sperm cells and live specimens from lab-made cultures) samples.

physics.optics↗

arXiv2024

Characterizing the Broadband Reflection Spectrum of MAXI J1803-298 During its 2021 Outburst with NuSTAR and NICER

MAXI J1803-298 is a transient black hole candidate discovered in May of 2021 during an outburst that lasted several months. Multiple X-ray observations reveal recurring "dipping" intervals in several of its light curves, particularly during the hard/intermediate states, with a typical recurrence period of $\sim7\,\mathrm{hours}$. We report analysis of four NuSTAR observations of the source, supplemented with NICER data where available, over the duration of the outburst evolution covering the hard, intermediate and the soft states. Reflection spectroscopy reveals the black hole to be rapidly spinning ($a_*=0.990\pm{0.001}$) with a near edge-on viewing angle ($i=70\pm{1}\deg$). Additionally, we show that the light-curve dips are caused by photo-electric absorption from a moderately ionized absorber whose origin is not fully understood, although it is likely linked to material from the companion star impacting the outer edges of the accretion disk. We further detect absorption lines in some of the spectra, potentially associated with Fe XXV and Fe XXVI, indicative of disk winds with moderate to extreme velocities. During the intermediate state and just before transitioning into the soft state, the source showed a sudden flux increase which we found to be dominated by soft disk photons and consistent with the filling of the inner accretion disk, at the onset of state transition. In the soft state, we show that models of disk self-irradiation provide a better fit and a preferred explanation to the broadband reflection spectrum, consistent with previous studies of other accreting sources.

astro-ph.HE↗

arXiv2024

Self-Consistent Disk-Reflection Analysis of the Black-Hole Candidate X-ray Binary MAXI J1813-095 with NICER, Swift, Chandra, and NuSTAR

We present our analysis of MAXI J1813-095 during its hard state ``stalled'' outburst in 2018. This self-consistent analysis has been carried out using \NICER, \Swift, \Chandra, and {\NuSTAR} throughout seven observations of MAXI J1813-095. We find a relativistic iron line at $\sim$6.5 keV from the inner region of the accretion disk. Our results are consistent with a slightly truncated disk or non-truncated disk for an inner radius of $\sim$2$R_\mathrm{g}$ and minimum spin of $>$0.7 with a best value of $\sim0.9$, assuming $R_\mathrm{in}$ reaches the innermost stable circular orbit at $\it{L_\mathrm{x}}$ $\sim$ 1\% $\it{L_\mathrm{Edd}}$. We analyzed MAXI J1813-095 over its outburst employing a spectral model which self-consistently couples the seed disk photons to the Comptonization and reflection components, also inclusive of reflection Comptonization. The unique aspect of this work is a reflection fraction of order unity, which is significantly higher than previous studies of this source, and is a consequence of applying the self-consistent disk-Comptonization-reflection spectral model. Other key parameters such as inclination and inner radius are found to be consistent with other works. works.

astro-ph.HE↗

arXiv2024

On the two-dimensional harmonic oscillator with an electric field confined to a circular box

We revisit the quantum-mechanical two-dimensional harmonic oscillator with an electric field confined to a circular box of impenetrable walls. In order to obtain the energy spectrum we resort to the Rayleigh-Ritz method with polynomial and Gaussian basis sets. We compare present results with those derived recently by other authors. We discuss the limits of large and small box radius and also do some calculations with perturbation theory.

quant-ph↗

arXiv2024

Investigating the Ultra-Compact X-ray Binary Candidate SLX 1735-269 with NICER and NuSTAR

We present two simultaneous NICER and NuSTAR observations of the ultra-compact X-ray binary (UCXB) candidate SLX 1735-269 while the source was in two different spectral states. Using various reflection modeling techniques, we find that xillverCO, a model used for fitting X-ray spectra of UCXBs with high carbon and oxygen abundances is an improvement over relxill or relxillns, which instead contains solar-like chemical abundances. This provides indirect evidence in support of the source being ultra-compact. We also use this reflection model to get a preliminary measurement of the inclination of the system, $i = 57^{+23}_{-7}$ degrees. This is consistent with our timing analysis, where a lack of eclipses indicates an inclination of $i<80^{\circ}$. The timing analysis is otherwise inconclusive, and we can not confidently measure the orbital period of the system.

astro-ph.HE↗

arXiv2024

Evaluating the Uncertainty in Mean Residual Times: Estimators Based on Residence Times from Discrete Time Processes

In this work, we propose estimators for the uncertainty in mean residual times that require, for their evaluation, statistically independent individual residence times obtained from a discrete time process. We examine their performance through numerical experiments involving well-known probability distributions, and an application example using molecular dynamics simulation results, from an aqueous NaCl solution, is provided. These computationally inexpensive estimators, capable of achieving very accurate outcomes, serve as useful tools for assessing and reporting uncertainties in mean residual times across a wide range of simulations.

stat.ME↗

arXiv2024

Emergence of hot corona and truncated disk in simulations of accreting stellar mass black holes

Stellar mass black holes in X-ray binaries (XRBs) are known to display different states characterized by different spectral and timing properties, understood in the framework of a hot corona coexisting with a thin accretion disk whose inner edge is truncated. There are several open questions related to the nature and properties of the corona, the thin disk, and dynamics behind the hard state. This motivated us to perform two-dimensional hydrodynamical simulations of accretion flows onto a 10 solar masses black hole. We consider a two-temperature plasma, incorporate radiative cooling with bremmstrahlung, synchrotron and comptonization losses and approximate the Schwarzschild spacetime via a pseudo-Newtonian potential. We varied the mass accretion rate in the range 0.02 <= Mdot/Mdot_Edd <= 0.35. Our simulations show the natural emergence of a colder truncated thin disk embedded in a hot corona, as required to explain the hard state of XRBs. We found that as Mdot increases, the corona contracts and the inner edge of the thin disk gets closer to the event horizon. At a critical accretion rate 0.02 <= Mdot_crit\Mdot_Edd <= 0.06, the thin disk disappears entirely. We discuss how our simulations compare with XRB observations in the hard state.

astro-ph.HE↗

arXiv2024

X-ray Polarization of the Black Hole X-ray Binary 4U 1630-47 Challenges Standard Thin Accretion Disk Scenario

Large energy-dependent X-ray polarization degree is detected by the Imaging X-ray Polarimetry Explorer ({IXPE}) in the high-soft emission state of the black hole X-ray binary 4U 1630--47. The highly significant detection (at $\approx50σ$ confidence level) of an unexpectedly high polarization, rising from $\sim6\%$ at $2$ keV to $\sim10\%$ at $8$ keV, cannot be easily reconciled with standard models of thin accretion discs. In this work we compare the predictions of different theoretical models with the {IXPE} data and conclude that the observed polarization properties are compatible with a scenario in which matter accretes onto the black hole through a thin disc, covered by a partially-ionized atmosphere flowing away at mildly relativistic velocities.

astro-ph.HE↗

arXiv2024

On the eigenvalues of the harmonic oscillator with a Gaussian perturbation

We test the analytical expressions for the first two eigenvalues of the harmonic oscillator with a Gaussian perturbation proposed recently. Our numerical eigenvalues show that those expressions are valid in an interval of the coupling parameter that is greater than the one estimated by the authors. We also calculate critical values of the coupling parameter and several exceptional points in the complex plane.

quant-ph↗

arXiv2024

Reconfiguration of a 2D Structure Using Spatio-Temporal Planning and Load Transferring

We present progress on the problem of reconfiguring a 2D arrangement of building material by a cooperative group of robots. These robots must avoid collisions, deadlocks, and are subjected to the constraint of maintaining connectivity of the structure. We develop two reconfiguration methods, one based on spatio-temporal planning, and one based on target swapping, to increase building efficiency. The first method can significantly reduce planning times compared to other multi-robot planners. The second method helps to reduce the amount of time robots spend waiting for paths to be cleared, and the overall distance traveled by the robots.

cs.RO↗

arXiv2023

The High Energy X-ray Probe (HEX-P): Probing Accretion onto Stellar Mass Black Holes

Accretion is a universal astrophysical process that plays a key role in cosmic history, from the epoch of reionization to galaxy and stellar formation and evolution. Accreting stellar-mass black holes in X-ray binaries are one of the best laboratories to study the accretion process and probe strong gravity -- and most importantly, to measure the angular momentum, or spin, of black holes, and its role as a powering mechanism for relativistic astrophysical phenomena. Comprehensive characterization of the disk-corona system of accreting black holes, and their co-evolution, is fundamental to measurements of black hole spin. Here, we use simulated data to demonstrate how key unanswered questions in the study of accreting stellar-mass black holes will be addressed by the {\it High Energy X-ray Probe} (\hexp). \hexp\ is a probe-class mission concept that will combine high spatial resolution X-ray imaging and broad spectral coverage ($0.2\mbox{--}80$keV) with a sensitivity superior to current facilities (including \xmm\ and \nustar) to enable revolutionary new insights into a variety of important astrophysical problems. We illustrate the capability of \hexp\ to: 1) measure the evolving structures of black hole binary accretion flows down to low ($\lesssim0.1\%$) Eddington-scaled luminosities via detailed X-ray reflection spectroscopy; 2) provide unprecedented spectral observations of the coronal plasma, probing its elusive geometry and energetics; 3) perform detailed broadband studies of stellar mass black holes in nearby galaxies, thus expanding the repertoire of sources we can use to study accretion physics and determine the fundamental nature of black holes; and 4) act as a complementary observatory to a range of future ground and space-based astronomical observatories, thus providing key spectral measurements of the multi-component emission from the inner accretion flows of BH-XRBs.

astro-ph.HE↗