arXiv subjects

T. Heim

Publications and source records attributed to T. Heim.

8 recordsLinked to original sources

arXiv2025

Pixel column issue in the ATLAS Inner Tracker modules

Pixel modules are currently being built for the ATLAS ITk Pixel detector upgrade. During the preproduction phase, recurring chip malfunctioning was observed during electrical testing. It was possible to bypass this issue by disabling some pixel core columns in the ITkPix readout chip. Therefore the issue is called "core column issue" which is a direct disqualifier for a pixel module. A concerning number of cases has been observed in pixel modules with ITkPix v1.1 as well as v2 chips which significantly impacts the module yield. However, the behaviour is erratic and there is not any evidence hinting at the origin of this issue. These proceedings outline the investigations of the issue, highlighting the electrical behaviour during testing, present findings from the data collected via our production database and through visual inspection, and point towards possible causes of the issue.

physics.ins-det↗

arXiv2022

Solid State Detectors and Tracking for Snowmass

Tracking detectors are of vital importance for collider-based high energy physics (HEP) experiments. The primary purpose of tracking detectors is the precise reconstruction of charged particle trajectories and the reconstruction of secondary vertices. The performance requirements from the community posed by the future collider experiments require an evolution of tracking systems, necessitating the development of new techniques, materials and technologies in order to fully exploit their physics potential. In this article we summarize the discussions and conclusions of the 2022 Snowmass Instrumentation Frontier subgroup on Solid State and Tracking Detectors (Snowmass IF03).

physics.ins-det↗

arXiv2022

Enabling Capabilities for Infrastructure and Workforce in Electronics and ASICs

The impressive progress in data rate capabilities, pattern recognition, and spatial resolution of current detectors in experimental particle physics has been possible thanks to the availability of sophisticated analog processors combined with complex digital signal processors implemented in custom made front end ASICs. The demands in terms of performance and increasingly smaller feature sizes are significant. In order to meet these instrumentation challenges, we need to educate and retain a skilled work force, as well as aggregate design tools and acquired knowledge. We propose a multifaceted initiative to ensure that these needs are met.

physics.ins-det↗

arXiv2006

Comment on: ``Solving the riddle of the bright mismatches: Labeling and effective binding in oligonucleotide arrays"

In a recent paper [Phys. Rev. E 68, 011906 (2003)], Naef and Magnasco suggested that the "bright" mismatches observed in Affymetrix microarray experiments are caused by the fluorescent molecules used to label RNA target sequences, which would impede target-probe hybridization. Their conclusion is based on the observation of "unexpected" asymmetries in the affinities obtained by fitting microarray data from publicly available experiments. We point out here that the observed asymmetry is due to the inequivalence of RNA and DNA, and that the reported affinities are consistent with stacking free energies obtained from melting experiments of unlabeled nucleic acids in solution. The conclusion of Naef and Magnasco is therefore based on an unjustified assumption.

q-bio.BM↗

arXiv2006

Physics-based analysis of Affymetrix microarray data

We analyze publicly available data on Affymetrix microarrays spike-in experiments on the human HGU133 chipset in which sequences are added in solution at known concentrations. The spike-in set contains sequences of bacterial, human and artificial origin. Our analysis is based on a recently introduced molecular-based model [E. Carlon and T. Heim, Physica A 362, 433 (2006)] which takes into account both probe-target hybridization and target-target partial hybridization in solution. The hybridization free energies are obtained from the nearest-neighbor model with experimentally determined parameters. The molecular-based model suggests a rescaling that should result in a "collapse" of the data at different concentrations into a single universal curve. We indeed find such a collapse, with the same parameters as obtained before for the older HGU95 chip set. The quality of the collapse varies according to the probe set considered. Artificial sequences, chosen by Affymetrix to be as different as possible from any other human genome sequence, generally show a much better collapse and thus a better agreement with the model than all other sequences. This suggests that the observed deviations from the predicted collapse are related to the choice of probes or have a biological origin, rather than being a problem with the proposed model.

q-bio.BM↗

arXiv2006

Effective affinities in microarray data

In the past couple of years several studies have shown that hybridization in Affymetrix DNA microarrays can be rather well understood on the basis of simple models of physical chemistry. In the majority of the cases a Langmuir isotherm was used to fit experimental data. Although there is a general consensus about this approach, some discrepancies between different studies are evident. For instance, some authors have fitted the hybridization affinities from the microarray fluorescent intensities, while others used affinities obtained from melting experiments in solution. The former approach yields fitted affinities that at first sight are only partially consistent with solution values. In this paper we show that this discrepancy exists only superficially: a sufficiently complete model provides effective affinities which are fully consistent with those fitted to experimental data. This link provides new insight on the relevant processes underlying the functioning of DNA microarrays.

q-bio.BM↗

arXiv2003

A Monte Carlo Calculation of the Pionium Break-up Probability with Different Sets of Pionium Target Cross Sections

Chiral Perturbation Theory predicts the lifetime of pionium, a hydrogen-like $π^+ π^-$ atom, to better than 3% precision. The goal of the DIRAC experiment at CERN is to obtain and check this value experimentally by measuring the break-up probability of pionium in a target. In order to accurately measure the lifetime one needs to know the relationship between the break-up probability and lifetime to a 1% accuracy. We have obtained this dependence by modeling the evolution of pionic atoms in the target using Monte Carlo methods. The model relies on the computation of the pionium--target atom interaction cross sections. Three different sets of pionium--target cross sections with varying degrees of complexity were used: from the simplest first order Born approximation involving only the electrostatic interaction to a more advanced approach taking into account multi-photon exchanges and relativistic effects. We conclude that in order to obtain the pionium lifetime to 1% accuracy from the break-up probability, the pionium--target cross sections must be known with the same accuracy for the low excited bound states of the pionic atom. This result has been achieved, for low $Z$ targets, with the two most precise cross section sets. For large $Z$ targets only the set accounting for multiphoton exchange satisfies the condition.

physics.atom-ph↗

arXiv1996

The morphological segregation of galaxies in clusters. III. The distant cluster Cl0939+4713 (Abell 851)

We have performed an isophotal analysis of galaxies in the distant (z=0.4) cluster Cl0939+4713 (Abell 851), using post-refurbished Hubble Space Telescope images. Morphological type estimates for the galaxies are given. A rigorous comparison of the properties of the types shows that early-type galaxies in Cl0939+4713 are, within the present statistical or systematic errors, indistinguishable from their counterparts in Coma in all their studied properties, namely ellipticity profile, slope of the color-magnitude relation from the near-ultraviolet to the near-infrared colors, mean surface brightness and luminosity function in the restframe photographic J band, homogeneity in color (around the color-magnitude relation). Furthermore ellipticals and lenticulars are separately homogeneous in their mean surface brightness, and have similar relative mean surface brightnesses in both clusters. Spirals are overabundant in Cl0939+4713 with respect to Coma, but twice less than previously estimated, and are more similar to field spirals than to cluster spirals. We suggest that the differences in the photometric properties of the spirals in the two clusters arise from differences in cluster gas density distribution which ultimately bring star formation in the spirals to a stop in Coma, but not in Cl0939+4713. The morphological types are segregated along a privileged direction that coincides with the position angle of the major axis of the outer X-ray isophotes in the cluster, just like in Coma and Perseus.

astro-ph↗