The Perfect Atom: Bound States of Supersymmetric Quantum Electrodynamics

We study hydrogen-like atoms in N=1 supersymmetric quantum electrodynamics with an electronic and a muonic family. These atoms are bound states of an anti-muon and an electron or their superpartners. The exchange of a photino converts different bound states into each other. We determine the energy eigenstates and calculate the spectrum to fourth order in the fine structure constant. A difference between these perfect atoms and non-supersymmetric ones is the absence of hyperfine structure. We organize the eigenstates into super multiplets of the underlying symmetry algebra.Comment: 30 pages, 2 figures. v2: mistake associated with gauge choice fixed, references added. v3: comment about super-positronium added, published versio

An X-ray Microscopy Study of the Microstructural Effects on Thermal Conductivity in Cast Aluminum-Copper Compounds

A metallurgical joint between aluminum and copper established by compound casting provides for high thermal conductivity, which is required for lightweight cooling solutions in applications such as high-power light-emitting diodes or computer processors. If casting is employed in a silane-doped inert gas atmosphere whose oxygen partial pressure is adequate to extreme high vacuum, reoxidation of the active surfaces of aluminum and copper is prevented, and thus a metallurgical bond can be created directly between aluminum and copper. With this approach, thermal conductivities as high as 88.3 W/m·K were realized. In addition, X-ray microscopy was used to shed light on the microstructure–thermal property relationship. It is demonstrated that both porosity and non-bonded areas have a substantial impact on the thermophysical properties of the compound zone. Based on the data obtained, casting parameters can be developed that provide for defect-free bonding zones and optimal heat transfer between the joining partners

Photon correlation spectroscopy with heterodyne mixing based on soft-x-ray magnetic circular dichroism

Many magnetic equilibrium states and phase transitions are characterized by fluctuations. Such magnetic fluctuation can in principle be detected with scattering-based x-ray photon correlation spectroscopy (XPCS). However, in the established approach of XPCS, the magnetic scattering signal is quadratic in the magnetic scattering cross section, which results not only in often prohibitively small signals but also in a fundamental inability to detect negative correlations (anticorrelations). Here, we propose to exploit the possibility of heterodyne mixing of the magnetic signal with static charge scattering to reconstruct the first-order (linear) magnetic correlation function. We show that the first-order magnetic scattering signal reconstructed from heterodyne scattering now directly represents the underlying magnetization texture. Moreover, we suggest a practical implementation based on an absorption mask rigidly connected to the sample, which not only produces a static charge scattering signal but also eliminates the problem of drift-induced artificial decay of the correlation functions. Our method thereby significantly broadens the range of scientific questions accessible by magnetic x-ray photon correlation spectroscopy

Coherent x-ray magnetic imaging with 5 nm resolution

Soft x-ray microscopy plays an important role in modern spintronics. However, the achievable resolution of most x-ray magnetic imaging experiments limits access to fundamental and technologically relevant length scales in the sub-10 nm regime. Here, we demonstrate x-ray magnetic microscopy with 5 nm resolution by combining holography-assisted coherent diffractive imaging with heterodyne amplification of the weak magnetic signal. The gain in resolution and contrast makes magnetic pinning sites visible and allows to measure the local width of domain walls. The ability to detect and map such properties with photons opens new horizons for elementspecific, time-resolved, and operando research on magnetic materials and beyond

Coherent correlation imaging for resolving fluctuating states of matter

Fluctuations and stochastic transitions are ubiquitous in nanometre-scale systems, especially in the presence of disorder. However, their direct observation has so far been impeded by a seemingly fundamental, signal-limited compromise between spatial and temporal resolution. Here we develop coherent correlation imaging (CCI) to overcome this dilemma. Our method begins by classifying recorded camera frames in Fourier space. Contrast and spatial resolution emerge by averaging selectively over same-state frames. Temporal resolution down to the acquisition time of a single frame arises independently from an exceptionally low misclassification rate, which we achieve by combining a correlation-based similarity metric1,2 with a modified, iterative hierarchical clustering algorithm3,4. We apply CCI to study previously inaccessible magnetic fluctuations in a highly degenerate magnetic stripe domain state with nanometre-scale resolution. We uncover an intricate network of transitions between more than 30 discrete states. Our spatiotemporal data enable us to reconstruct the pinning energy landscape and to thereby explain the dynamics observed on a microscopic level. CCI massively expands the potential of emerging high-coherence X-ray sources and paves the way for addressing large fundamental questions such as the contribution of pinning5–8 and topology9–12 in phase transitions and the role of spin and charge order fluctuations in high-temperature superconductivity13,14

The Lantern Vol. 62, No. 2, Summer 1995

• In the Season of Grief • Subtleties • Crazehaze • Blacksmith • I Feel Your Weight • L\u27Amour Manque • Sense of You • Greed • Gender (Rolled) • Soliloquy of a Punter • Nightmares • God is a Frisbee • Cleansing • Flat • Chemistry of Mind • Louderback • Ritual • Rebuilding Mother • Scott Lomba • The Acting Bug • Untitled • The Seek • Gluttony • Great South Bay • Archangel • Suburban Zeus • Vespers • At Change of A-Dress • The Hierarchy of Coolness • The Apology • I Know it is Evening There • Pridehttps://digitalcommons.ursinus.edu/lantern/1146/thumbnail.jp

The Extreme Hosts of Extreme Supernovae

We use GALEX ultraviolet (UV) and optical integrated photometry of the hosts of seventeen luminous supernovae (LSNe, having peak M_V < -21) and compare them to a sample of 26,000 galaxies from a cross-match between the SDSS DR4 spectral catalog and GALEX interim release 1.1. We place the LSNe hosts on the galaxy NUV-r versus M_r color magnitude diagram (CMD) with the larger sample to illustrate how extreme they are. The LSN hosts appear to favor low-density regions of the galaxy CMD falling on the blue edge of the blue cloud toward the low luminosity end. From the UV-optical photometry, we estimate the star formation history of the LSN hosts. The hosts have moderately low star formation rates (SFRs) and low stellar masses (M_*) resulting in high specific star formation rates (sSFR). Compared with the larger sample, the LSN hosts occupy low-density regions of a diagram plotting sSFR versus M_* in the area having higher sSFR and lower M_*. This preference for low M_*, high sSFR hosts implies the LSNe are produced by an effect having to do with their local environment. The correlation of mass with metallicity suggests that perhaps wind-driven mass loss is the factor that prevents LSNe from arising in higher-mass, higher-metallicity hosts. The massive progenitors of the LSNe (>100 M_sun), by appearing in low-SFR hosts, are potential tests for theories of the initial mass function that limit the maximum mass of a star based on the SFR.Comment: 8 pages, 3 figures, 2 tables, accepted to ApJ, amended references and updated SN designation

The Igf2/H19 imprinting control region exhibits sequence-specific and cell-type-dependent DNA methylation-mediated repression

Methylation of CpGs is generally thought to repress transcription without significant influence from the sequence surrounding the methylated dinucleotides. Using the mouse Igf2/H19 imprinting control region (ICR), Igf2r differentially methylated region 2 (DMR2) and bacterial sequences, we addressed how methylation-dependent repression (MDR) from a distance varies with CpG number, density and surrounding sequence. In stably transfected F9 cells, the methylated ICR repressed expression from a CpG-free reporter plasmid more than 1000-fold compared with its unmethylated control. A segment of pBluescript, with a CpG number equal to the ICR's but with a higher density, repressed expression only 70-fold when methylated. A bacteriophage lambda fragment and the Igf2r DMR2 showed minimal MDR activity, despite having CpG numbers and densities similar to or greater than the ICR. By rearranging or deleting CpGs, we identified CpGs associated with three CTCF sites in the ICR that are necessary and sufficient for sequence-specific MDR. In contrast to F9 cells, the methylated ICR and pBS fragments exhibited only 3-fold reporter repression in Hela cells and none in Cos7. Our results show that the strength of MDR from a distance can vary a 1000-fold between different cell types and depends on the sequence surrounding the methylated CpGs, but does not necessarily increase with CpG number or density

The Lantern Vol. 63, No. 1, Fall 1995

• The Birthday Celebration • Surprise! Surprise! • Oregold • Future of Parenthood #2 • Seeds • How I Spent My Summer Vacation • Random Scenes From 1/2 Hour at Work • Life in the Coal Mines • Driveway • Midnight in the Court of Kings • The Black Quadrilateral • People I Hate to See, But Refuse to Dismiss • Metropolized • Poetry in Motion • Dream #3 • Rhythms • Mercykilling • Untitled • Lupine Lord • At the Bottom of the Cup • House of Commons • Poetry I Can\u27t Standhttps://digitalcommons.ursinus.edu/lantern/1147/thumbnail.jp