Search for Dark Matter Annihilation Signals in the H.E.S.S. Inner Galaxy Survey.

The central region of the Milky Way is one of the foremost locations to look for dark matter (DM) signatures. We report the first results on a search for DM particle annihilation signals using new observations from an unprecedented γ-ray survey of the Galactic Center (GC) region, i.e., the Inner Galaxy Survey, at very high energies (≳100 GeV) performed with the H.E.S.S. array of five ground-based Cherenkov telescopes. No significant γ-ray excess is found in the search region of the 2014-2020 dataset and a profile likelihood ratio analysis is carried out to set exclusion limits on the annihilation cross section ⟨σv⟩. Assuming Einasto and Navarro-Frenk-White (NFW) DM density profiles at the GC, these constraints are the strongest obtained so far in the TeV DM mass range. For the Einasto profile, the constraints reach ⟨σv⟩ values of 3.7×10^{-26} cm^{3} s^{-1} for 1.5 TeV DM mass in the W^{+}W^{-} annihilation channel, and 1.2×10^{-26} cm^{3} s^{-1} for 0.7 TeV DM mass in the τ^{+}τ^{-} annihilation channel. With the H.E.S.S. Inner Galaxy Survey, ground-based γ-ray observations thus probe ⟨σv⟩ values expected from thermal-relic annihilating TeV DM particles.

Quantitative region-of-interest tomography using variable field of view.

In X-ray computed tomography, the task of imaging only a local region of interest (ROI) inside a larger sample is very important. However, without a priori information, this ROI cannot be exactly reconstructed using only the image data limited to the ROI. We propose here an approach of region-of-interest tomography, which reconstructs a ROI within an object from projections of different fields of view acquired on a specific angular sampling scheme in the same tomographic experiment. We present a stable procedure that not only yields high-quality images of the ROI but keeps as well the quantitative contrast on the reconstructed images. In addition, we analyze the minimum number of projections required for ROI tomography from the point of view of the band region of the Radon transform, which confirms this number must be estimated based on the size of the entire object and not only on the size of the ROI.

High-resolution three-dimensional imaging of topological textures in nanoscale single-diamond networks.

Topological defects-extended lattice deformations that are robust against local defects and annealing-have been exploited to engineer novel properties in both hard and soft materials. Yet, their formation kinetics and nanoscale three-dimensional structure are poorly understood, impeding their benefits for nanofabrication. We describe the fabrication of a pair of topological defects in the volume of a single-diamond network (space group Fd 3 ¯ m) templated into gold from a triblock terpolymer crystal. Using X-ray nanotomography, we resolve the three-dimensional structure of nearly 70,000 individual single-diamond unit cells with a spatial resolution of 11.2 nm, allowing analysis of the long-range order of the network. The defects observed morphologically resemble the comet and trefoil patterns of equal and opposite half-integer topological charges observed in liquid crystals. Yet our analysis of strain in the network suggests typical hard matter behaviour. Our analysis approach does not require a priori knowledge of the expected positions of the nodes in three-dimensional nanostructured systems, allowing the identification of distorted morphologies and defects in large samples.

Attosecond electron wave-packet interference observed by transient absorption.

We perform attosecond time-resolved transient absorption spectroscopy around the first ionization threshold of helium and observe rapid oscillations of the absorption of the individual harmonics as a function of time delay with respect to a superimposed, moderately strong infrared laser field. The phase relation between the absorption modulation of individual harmonics gives direct evidence for the interference of transiently bound electronic wave packets as the mechanism behind the absorption modulation.

Spatial fingerprint of quantum path interferences in high order harmonic generation.

We have spatially and spectrally resolved the high order harmonic emission from an argon gas target. Under proper phase matching conditions we were able to observe for the first time the spatial fine structure originating from the interference of the two shortest quantum paths in the harmonic beam. The structure can be explained by the intensity-dependent harmonic phase of the contributions from the two paths. The spatially and spectrally resolved measurements are consistent with previous spatially integrated results. Our measurement method represents a new tool to clearly distinguish between different interference effects and to potentially observe higher order trajectories in the future with improved detection sensitivity. Here, we demonstrate additional experimental evidence that the observed interference pattern is only due to quantum-path interferences and cannot be explained by a phase modulation effect. Our experimental results are fully supported by simulations using the strong field approximation and including propagation.

A Convex Variational Model for Learning Convolutional Image Atoms from Incomplete Data.

A variational model for learning convolutional image atoms from corrupted and/or incomplete data is introduced and analyzed both in function space and numerically. Building on lifting and relaxation strategies, the proposed approach is convex and allows for simultaneous image reconstruction and atom learning in a general, inverse problems context. Further, motivated by an improved numerical performance, also a semi-convex variant is included in the analysis and the experiments of the paper. For both settings, fundamental analytical properties allowing in particular to ensure well-posedness and stability results for inverse problems are proven in a continuous setting. Exploiting convexity, globally optimal solutions are further computed numerically for applications with incomplete, noisy and blurry data and numerical results are shown.

Ionization effects on spectral signatures of quantum-path interference in high-harmonic generation.

The interference between the emission originating from the short and long electron quantum paths is intrinsic to the high harmonic generation process. We investigate the universal properties of these quantum-path interferences in various generation media and discuss how ionization effects influence the observed interference structures. Our comparison of quantum-path interferences observed in xenon, argon, and neon demonstrates that our experimental tools are generally applicable and should also allow investigating more complex systems such as molecules or clusters.

OMNY-A tOMography Nano crYo stage.

For many scientific questions gaining three-dimensional insight into a specimen can provide valuable information. We here present an instrument called "tOMography Nano crYo (OMNY)," dedicated to high resolution 3D scanning x-ray microscopy at cryogenic conditions via hard X-ray ptychography. Ptychography is a lens-less imaging method requiring accurate sample positioning. In OMNY, this in achieved via dedicated laser interferometry and closed-loop position control reaching sub-10 nm positioning accuracy. Cryogenic sample conditions are maintained via conductive cooling. 90 K can be reached when using liquid nitrogen as coolant, and 10 K is possible with liquid helium. A cryogenic sample-change mechanism permits measurements of cryogenically fixed specimens. We compare images obtained with OMNY with older measurements performed using a nitrogen gas cryo-jet of stained, epoxy-embedded retina tissue and of frozen-hydrated Chlamydomonas cells.

Spatio-temporal characterization of few-cycle pulses obtained by filamentation.

Intense sub-5-fs pulses were generated by filamentation in a noble gas and subsequent chirped-mirror pulse compression. The transversal spatial dependence of the temporal pulse profile was investigated by spatial selection of parts of the output beam. Selecting the central core of the beam is required for obtaining the shortest possible pulses. Higher energy efficiency is only obtained at the expense of pulse contrast since towards the outer parts of the beam the energy is spread into satellite structures leading to a double-pulse profile on the very off-axis part of the beam. Depending on the requirements for a particular application, a trade-off between the pulse duration and the pulse energy has to be done. The energy of the sub-5-fs pulses produced was sufficient for the generation of high order harmonics in Argon. In addition, full simulation is performed in space and time on pulse propagation through filamentation that explains the double-pulse structure observed as part of a conical emission enhanced by the plasma defocusing.

Clinical Application of Fiber Visualization with LIC Maps Using Multidirectional Anisotropic Glyph Samples (A-Glyph LIC).

Recently, a fiber visualization method for high-angular resolution diffusion-weighted magnetic resonance imaging (MRI) data was proposed using a multiple-kernel line integral convolution (LIC) algorithm and an anisotropic spot pattern. This processing routine leads to high contrast color-coded LIC maps that are capable of visualizing local anisotropy information and regional fiber architecture. In this paper, we evaluate and validate this method by applying it to simulated datasets and to in vivo diffusion MRI data of children and adults with different disease conditions and healthy volunteers. Compared to routine clinical fiber visualization (color-coded fractional anisotropy, FA maps, and fiber tractography), it has the advantage of visualizing complex local fiber architecture in a fully automated way. The results indicate that this method is capable of reliably delineating normal fiber architecture and fibers infiltrated, displaced, or disrupted by lesions and is therefore a promising tool in the clinical context.

Three-Dimensional Imaging of Biological Tissue by Cryo X-Ray Ptychography.

High-throughput three-dimensional cryogenic imaging of thick biological specimens is valuable for identifying biologically- or pathologically-relevant features of interest, especially for subsequent correlative studies. Unfortunately, high-resolution imaging techniques at cryogenic conditions often require sample reduction through sequential physical milling or sectioning for sufficient penetration to generate each image of the 3-D stack. This study represents the first demonstration of using ptychographic hard X-ray tomography at cryogenic temperatures for imaging thick biological tissue in a chemically-fixed, frozen-hydrated state without heavy metal staining and organic solvents. Applied to mammalian brain, this label-free cryogenic imaging method allows visualization of myelinated axons and sub-cellular features such as age-related pigmented cellular inclusions at a spatial resolution of ~100 nanometers and thicknesses approaching 100 microns. Because our approach does not require dehydration, staining or reduction of the sample, we introduce the possibility for subsequent analysis of the same tissue using orthogonal approaches that are expected to yield direct complementary insight to the biological features of interest.

OMNY PIN-A versatile sample holder for tomographic measurements at room and cryogenic temperatures.

Nowadays ptychographic tomography in the hard x-ray regime, i.e., at energies above about 2 keV, is a well-established measurement technique. At the Paul Scherrer Institut, currently two instruments are available: one is measuring at room temperature and atmospheric pressure, and the other, the so-called OMNY (tOMography Nano crYo) instrument, is operating at ultra-high vacuum and offering cryogenic sample temperatures down to 10 K. In this manuscript, we present the sample mounts that were developed for these instruments. Aside from excellent mechanical stability and thermal conductivity, they also offer highly reproducible mounting. Various types were developed for different kinds of samples and are presented in detail, including examples of how specimens can be mounted on these holders. We also show the first hard x-ray ptychographic tomography measurements of high-pressure frozen biological samples, in the present case Chlamydomonas cells, the related sample pins and preparation steps. For completeness, we present accessories such as transportation containers for both room temperature and cryogenic samples and a gripper mechanism for automatic sample changing. The sample mounts are not limited to x-ray tomography or hard x-ray energies, and we believe that they can be very useful for other instrumentation projects.

A three-dimensional view of structural changes caused by deactivation of fluid catalytic cracking catalysts.

Since its commercial introduction three-quarters of a century ago, fluid catalytic cracking has been one of the most important conversion processes in the petroleum industry. In this process, porous composites composed of zeolite and clay crack the heavy fractions in crude oil into transportation fuel and petrochemical feedstocks. Yet, over time the catalytic activity of these composite particles decreases. Here, we report on ptychographic tomography, diffraction, and fluorescence tomography, as well as electron microscopy measurements, which elucidate the structural changes that lead to catalyst deactivation. In combination, these measurements reveal zeolite amorphization and distinct structural changes on the particle exterior as the driving forces behind catalyst deactivation. Amorphization of zeolites, in particular, close to the particle exterior, results in a reduction of catalytic capacity. A concretion of the outermost particle layer into a dense amorphous silica-alumina shell further reduces the mass transport to the active sites within the composite.Catalyst deactivation in fluid catalytic cracking processes is unavoidably associated with structural changes. Here, the authors visualize the deactivation of zeolite catalysts by ptychography and other imaging techniques, showing pronounced amorphization of the outer layer of the catalyst particles.

Image-Based Personalization of Cardiac Anatomy for Coupled Electromechanical Modeling.

Computational models of cardiac electromechanics (EM) are increasingly being applied to clinical problems, with patient-specific models being generated from high fidelity imaging and used to simulate patient physiology, pathophysiology and response to treatment. Current structured meshes are limited in their ability to fully represent the detailed anatomical data available from clinical images and capture complex and varied anatomy with limited geometric accuracy. In this paper, we review the state of the art in image-based personalization of cardiac anatomy for biophysically detailed, strongly coupled EM modeling, and present our own tools for the automatic building of anatomically and structurally accurate patient-specific models. Our method relies on using high resolution unstructured meshes for discretizing both physics, electrophysiology and mechanics, in combination with efficient, strongly scalable solvers necessary to deal with the computational load imposed by the large number of degrees of freedom of these meshes. These tools permit automated anatomical model generation and strongly coupled EM simulations at an unprecedented level of anatomical and biophysical detail.

Improving organic tandem solar cells based on water-processed nanoparticles by quantitative 3D nanoimaging.

Organic solar cells have great potential for upscaling due to roll-to-roll processing and a low energy payback time, making them an attractive sustainable energy source for the future. Active layers coated with water-dispersible Landfester particles enable greater control of the layer formation and easier access to the printing industry, which has reduced the use of organic solvents since the 1980s. Through ptychographic X-ray computed tomography (PXCT), we image quantitatively a roll-to-roll coated photovoltaic tandem stack consisting of one bulk heterojunction active layer and one Landfester particle active layer. We extract the layered morphology with structural and density information including the porosity present in the various layers and the silver electrode with high resolution in 3D. The Landfester particle layer is found to have an undesired morphology with negatively correlated top- and bottom interfaces, wide thickness distribution and only partial surface coverage causing electric short circuits through the layer. By top coating a polymer material onto the Landfester nanoparticles we eliminate the structural defects of the layer such as porosity and roughness, and achieve the increased performance larger than 1 V expected for a tandem cell. This study highlights that quantitative imaging of weakly scattering stacked layers of organic materials has become feasible by PXCT, and that this information cannot be obtained by other methods. In the present study, this technique specifically reveals the need to improve the coatability and layer formation of Landfester nanoparticles, thus allowing improved solar cells to be produced.

Eicosanoids in rat brain during ischemia and reperfusion--correlation to DC depolarization.

The effects of complete ischemia on cerebral arachidonic acid (AA) metabolism were investigated in the isolated perfused rat brain. During 12.5 min of ischemia, AA, 5-hydroxy-6,8,11,14-eicosatetraenoic acid, and 15-hydroxy-5,8,11,13-eicosatetraenoic acid increased 129-, 4-, and 10-fold, respectively, while subsequent reperfusion for 30 min resulted in normalized levels independently of the duration of preceding ischemia. Prostaglandin (PG) F2 alpha, PGE2, PGD2, 6-keto-PGF1 alpha, and thromboxane (Tx) B2 remained at preischemic levels during 12.5 min of complete ischemia. However, at the end of subsequent reperfusion for 30 min, the levels of the prostanoids PGF2 alpha, PGE2, PGD2, 6-keto-PGF1 alpha, and TxB2 increased according to the preceding ischemic time. The levels reached a maximum after 7.5 min of ischemia and were elevated by 7-, 14-, 48-, 3-, and 30-fold, respectively. A prolongation of ischemia of up to 12.5 min was not associated with further increases of prostanoids at the end of reperfusion. The mechanisms underlying the metabolism of eicosanoids are discussed in relation to the changes of cortical direct current potential.

The interactions of propranolol and ketanserin.

Ten healthy volunteers received a single 10 mg intravenous dose of the 5-hydroxytryptamine-2 serotonin antagonist ketanserin in the control state and again during coadministration of propranolol, 80 mg b.i.d. There were no differences between control and propranolol treatment conditions in ketanserin volume of distribution (5.2 vs. 3.8 L/kg), elimination half-life (6.6 vs. 4.7 hours), clearance (9.7 vs. 10.0 ml/min/kg), or 72-hour excretion of intact ketanserin (0.7% vs. 0.7% of dose) or ketanserinol (21.8% vs. 24.9% of dose). In a second study, eight volunteers received a 160 mg oral dose of propranolol hydrochloride in the control state and again during treatment with ketanserin, 40 mg b.i.d. There were no significant differences between control and ketanserin conditions in the time of peak serum propranolol concentration (2.1 vs. 1.5 hours after dosage) or elimination half-life (3.8 vs. 4.1 hours). However, ketanserin increased peak serum propranolol concentrations (169 vs. 233 ng/ml) and reduced oral clearance (39 vs. 27 ml/min/kg); the differences were not statistically significant (0.05 less than P less than 0.1) with a sample size of eight. Thus therapeutic doses of propranolol in healthy volunteers do not alter the kinetics of a single dose of ketanserin. Therapeutic doses of ketanserin may impair oral clearance of propranolol, leading to increased area under the serum concentration curve and higher peak serum levels.

Studies on the intracerebral metabolism of anticonvulsant drugs--I. Perfusion of primidone through the isolated brain of the rat.

Primidone and phenobarbital (each 85 nmoles/ml were separately perfused through the isolated brain of the rat. After 5 min of perfusion similar amounts of primidone and phenobarbital were taken up into the brain; for both drugs the concentration ratio between brain and perfusion medium was about 0.2. However, after 2 hr of perfusion the mean concentration ratio for primidone was about 0.55; for phenobarbital it was about 0.9 thus indicating a better uptake of phenobarbital. In two regions (hypophysis, mesencephalon) the concentration of phenobarbital was significantly higher than in perfusion medium. During 2 hr of perfusion of primidone, substantial quantities of phenobarbital and PEMA were formed amounting to 1400 pmoles for each metabolite. The highest concentration of the metabolites was found in septum, hypothalamus, hypophysis and mesencephalon. The in situ metabolism of primidone in the intact brain was demonstrated for the first time.

Studies on the intracerebral metabolism of anticonvulsant drugs--II. Disposition of carbamazepine in the isolated perfused rat brain.

Carbamazepine (CBZ) was perfused (85 nmoles/ml) through the isolated brains of rats. After 2 hr the mean regional concentrations of the drug were between 170 and 234 nmoles/g wet weight. The total brain content of CBZ was 390 nmoles. During perfusion 82 nmoles epoxycarbamazepine (E-CBZ) were formed, most of which were found in perfusion medium. Tissue levels of E-CBZ were between 0.3 and 2.8 nmoles/g wet weight. No dihydroxycarbamazepine (DH-CBZ) could be found. Pretreatment of the rats with phenobarbital neither influenced the uptake of CBZ into the brains nor increased the formation of E-CBZ significantly.

(E)-1-alkyl-4-

(E)-1-Alkyl-4-[2-(alkylsulfonyl)-1-ethenyl]pyridinium salts were synthesized in two steps. These sulfones were stable at pH 7.3 and underwent a nucleophilic vinylic substitution (S(N)V) with mercaptans, including thiouracile, to give the corresponding 4-(thiovinyl)-pyridinium salts. The X-ray diffraction structure of (E)-1-methyl-4-[2-(ethylsulfanyl)-1-ethenyl]pyridinium iodide indicated conjugation of the sulfur with the pyridinium ring. (Z)-1-Methyl-4-[2-(methylsulfanyl)-1-ethenyl]pyridinium iodide, prepared from the corresponding thioether by reaction with methyl iodide in diethyl ether, underwent isomerization to the E isomer in a first-order reaction in deuterated [D6]DMSO with an activation energy of 14 kcalmol(-1). At pH 7, the (E)-1-methyl-4-[2-(methylsulfonyl)-1-ethenyl]pyridinium iodide (19) reacted specifically with thiols. The reaction of this sulfone with glutathione in a TES buffer at pH 7 was a second-order reaction (k = 4,100 M(-1)s(-1) at 30 degrees C) and gave the corresponding substitution product with an intense long wavelength absorption band (lambdamax=360 nm, epsilon = 27,500 M(-1)cm(-1)). The modification of different enzymes of known structure with 19 showed the high selectivity of this reagent towards thiol groups and its usefulness in the quantitative determination of free thiol groups in proteins.