Vectors in a Box

For an integer d>=1, let tau(d) be the smallest integer with the following property: If v1,v2,...,vt is a sequence of t>=2 vectors in [-1,1]^d with v1+v2+...+vt in [-1,1]^d, then there is a subset S of {1,2,...,t} of indices, 2<=|S|<=tau(d), such that \sum_{i\in S} vi is in [-1,1]^d. The quantity tau(d) was introduced by Dash, Fukasawa, and G\"unl\"uk, who showed that tau(2)=2, tau(3)=4, and tau(d)=Omega(2^d), and asked whether tau(d) is finite for all d. Using the Steinitz lemma, in a quantitative version due to Grinberg and Sevastyanov, we prove an upper bound of tau(d) <= d^{d+o(d)}, and based on a construction of Alon and Vu, whose main idea goes back to Hastad, we obtain a lower bound of tau(d)>= d^{d/2-o(d)}. These results contribute to understanding the master equality polyhedron with multiple rows defined by Dash et al., which is a "universal" polyhedron encoding valid cutting planes for integer programs (this line of research was started by Gomory in the late 1960s). In particular, the upper bound on tau(d) implies a pseudo-polynomial running time for an algorithm of Dash et al. for integer programming with a fixed number of constraints. The algorithm consists in solving a linear program, and it provides an alternative to a 1981 dynamic programming algorithm of Papadimitriou.Comment: 12 pages, 1 figur

Atmospheric neutron measurements with the SONTRAC science model

–The SOlar Neutron TRACking (SONTRAC) telescope was originally developed to measure the energy spectrum and incident direction of neutrons produced in solar flares, in the energy range 20 - 250 MeV. While developed primarily for solar physics, the SONTRAC detector may be employed in virtually any application requiring both energy measurement and imaging capabilities. The SONTRAC Science Model (SM) is presently being operated at the University of New Hampshire (UNH) as a ground-based instrument to investigate the energy spectrum, zenith and azimuth angle dependence of the cosmic-ray induced sea-level atmospheric neutron flux. SONTRAC measurements are based on the non-relativistic double scatter of neutrons off ambient protons within a block of scintillating fibers. Using the n-p elastic double-scatter technique, it is possible to uniquely determine the neutron’s energy and direction on an event-by-event basis. The 3D SM consists of a cube of orthogonal plastic scintillating fiber layers with 5 cm sides, read out by two CCD cameras. Two orthogonal imaging chains allow full 3D reconstruction of scattered proton tracks

Home sweet Home? : Erkenntnisse zu Homeoffice in den Zürcher Gemeindeverwaltungen während der Covid-19 Pandemie

Zur Eindämmung der Covid-19 Pandemie gab der Bundesrat zu Beginn des Jahres 2020 eine Homeoffice-Empfehlung ab. Anfang 2021 trat eine Homeoffice-Pflicht in Kraft. Frühere Studien zeigten, dass zu Beginn der Pandemie insbesondere auf Gemeindeebene jedoch nur sehr wenige Mitarbeiterinnen und Mitarbeiter im Homeoffice arbeiteten. In dieser Studie wird deshalb aus Sicht der Mitarbeiterinnen und Mitarbeiter untersucht, welche Voraussetzungen es für Homeoffice braucht, welche Auswirkungen mit Homeoffice verbunden werden und welche Rahmenbedingungen zukünftig aus Sicht der Gemeindeangestellten für Homeoffice vorhanden sein sollten. Zur Beantwortung dieser Fragen wurden im November 2020 Mitarbeiterinnen und Mitarbeiter von allen 162 Zürcher Gemeindeverwaltungen mittels einer standardisierten Online-Umfrage zu Homeoffice befragt. Die Befragung der Mitarbeiterinnen und Mitarbeiter zeigt, dass mit Beginn der Pandemie der Wunsch nach Homeoffice sowie auch die Nutzungsmöglichkeiten gestiegen sind. Als wichtige Aspekte zeigen sich die Eignung der Tätigkeit sowie die Eignung des heimischen Arbeitsplatzes. Negative Auswirkungen von Homeoffice sehen die Befragten insbesondere in der generellen Schwächung interpersoneller Beziehungen im beruflichen Umfeld. Positiv wiederum wirkt sich das Homeoffice auf die Vereinbarkeit von Beruf und Privatleben, auf das konzentrierte Arbeiten sowie auf die wahrgenommene Arbeitgeberattraktivität aus. Soll Homeoffice stärker genutzt werden, gilt es aus Sicht der Befragten zukünftig verstärkt flexibles Arbeiten zu ermöglichen, mehr digitale und interaktive Kommunikationsmittel zu nutzen und verstärkt in Teamentwicklungsmassahmen zu investieren. Insgesamt zeigen die Ergebnisse, dass es für erfolgreiches Homeoffice auf Gemeindestufe verstärkte Bemühungen bei der digitalen Transformation der öffentlichen Verwaltung sowie die Förderung eines beziehungsorientierten Führungsstils braucht

On the Role of Dendritic Cells in Peripheral T Cell Tolerance and Modulation of Autoimmunity

Recently, it has become clear that dendritic cells (DCs) are essential for the priming of T cell responses. However, their role in the maintenance of peripheral T cell tolerance remains largely undefined. Herein, an antigen-presenting cell (APC) transfer system was devised and applied to experimental allergic encephalomyelitis (EAE), to evaluate the contribution that DCs play in peripheral T cell tolerance. The CD8α−CD4+ subset, a minor population among splenic DCs, was found to mediate both tolerance and bystander suppression against diverse T cell specificities. Aggregated (agg) Ig-myelin oligodendrocyte glycoprotein (MOG), an Ig chimera carrying the MOG 35–55 peptide, binds and cross-links FcγR on APC leading to efficient peptide presentation and interleukin (IL)-10 production. Furthermore, administration of agg Ig-MOG into diseased mice induces relief from clinical EAE involving multiple epitopes. Such recovery could not occur in FcγR-deficient mice where both uptake of Ig-MOG and IL-10 production are compromised. However, reconstitution of these mice with DC populations incorporating the CD8α−CD4+ subset restored Ig-MOG–mediated reversal of EAE. Transfer of CD8α+ or even CD8α−CD4− DCs had no effect on the disease. These findings strongly implicate DCs in peripheral tolerance and emphasize their functional potency, as a small population of DCs was able to support effective suppression of autoimmunity

Momentum for Catalysis: How Surface Reactions Shape the RuO2 Flat Surface State

The active (110) surface of the benchmark oxygen evolution catalyst RuO2 spans a flat-band surface state (FBSS) between the surface projections of its Dirac nodal lines (DNLs) that define the electronic properties of this functional semimetal. Monitoring well-known surface adsorption processes of H2, O2, NO, and CO by in operando angle-resolved photoemission spectroscopy, we selectively modify the oxidation state of individual Ru surface sites and identify the electronic nature of the FBSS: stabilized by bridging oxygen Obr pz, the FBSS disperses along ⟨001⟩ oriented chains of bridging Rubr 4dz2 orbitals, collapses upon Obr removal, yet remains surprisingly unaffected by the oxidation state of the undercoordinated 1f-cus-Ru species. This directly reflects in the ability of RuO2(110) to oxidize CO and H2 along with its inability to oxidize NO, demonstrating the FBSS’s active role in catalytic charge transfer processes at the oxygen bridge sites. Our synergetic approach provides momentum-resolved insights to the interplay of a catalyst’s delocalized electronic band structure and the localized orbitals of its surface reactantsa route toward a microscopic understanding of heterogeneous catalysis

Thin channel β-Ga2O3 MOSFETs with self-aligned refractory metal gates

We report the first demonstration of self-aligned gate (SAG) β-Ga2O3 metal-oxide-semiconductor field-effect transistors (MOSFETs) as a path toward eliminating source access resistance for low-loss power applications. The SAG process is implemented with a subtractively defined and etched refractory metal, such as Tungsten, combined with ion-implantation. We report experimental and modeled DC performance of a representative SAG device that achieved a maximum transconductance of 35 mS mm-1 and an on-resistance of ∼30 Ω mm with a 2.5 μm gate length. These results highlight the advantage of implant technology for SAG β-Ga2O3 MOSFETs enabling future power switching and RF devices with low parasitic resistance. © Not subject to copyright in the USA. Contribution of Wright-Patterson AFB

High-throughput full-automatic synchrotron-based tomographic microscopy

The automatization tools for high-throughput tomographic microscopy developed at the TOMCAT beamline of the Swiss Light Source are describe