Accurate evaluation of hadronic uncertainties in spin-independent WIMP-nucleon scattering: Disentangling two- and three-flavor effects

We show how to avoid unnecessary and uncontrolled assumptions usually made in the literature about soft SU(3) flavor symmetry breaking in determining the two-flavor nucleon matrix elements relevant for direct detection of weakly interacting massive particles (WIMPs). Based on SU(2) chiral perturbation theory, we provide expressions for the proton and neutron scalar couplings fp,nu and fp,nd with the pion-nucleon σ term as the only free parameter, which should be used in the analysis of direct detection experiments. This approach for the first time allows for an accurate assessment of hadronic uncertainties in spin-independent WIMP-nucleon scattering and for a reliable calculation of isospin-violating effects. We find that the traditional determinations of Vfpu−fnu and fpd−fnd are off by a factor of 2.

Remote Effects Modulating the Spin Equilibrium of the Resting State of Cytochrome P450cam –An Investigation Using Active Site Analogues

The crystal structure of the resting state of cytochrome P450cam (CYP101), a heme thiolate protein, shows a cluster of six water molecules in the substrate binding pocket, one of which is coordinating to iron(III) as sixth ligand. The resting state is low-spin and changes to high-spin when substrate camphor binds and H2O is removed. In contrast to the protein, previously synthesised enzyme models such as H2O[BOND]FeIII(porph)(ArS−) were shown to be purely high-spin. Iron(S−)porphyrins with different distal sites mimicking proposed remote effects have been prepared and studied by cw-EPR. The results indicate that the low-spin of the resting state of P450cam is due to the fact that the water molecule coordinating to iron has an OH−-like character because of hydrogen bonding and polarisation of the water cluster, respectively.

Focal Epilepsy: MR Imaging of Nonhemodynamic Field Effects by Using a Phase-cycled Stimulus-induced Rotary Saturation Approach with Spin-Lock Preparation.

Purpose To investigate whether nonhemodynamic resonant saturation effects can be detected in patients with focal epilepsy by using a phase-cycled stimulus-induced rotary saturation (PC-SIRS) approach with spin-lock (SL) preparation and whether they colocalize with the seizure onset zone and surface interictal epileptiform discharges (IED). Materials and Methods The study was approved by the local ethics committee, and all subjects gave written informed consent. Eight patients with focal epilepsy undergoing presurgical surface and intracranial electroencephalography (EEG) underwent magnetic resonance (MR) imaging at 3 T with a whole-brain PC-SIRS imaging sequence with alternating SL-on and SL-off and two-dimensional echo-planar readout. The power of the SL radiofrequency pulse was set to 120 Hz to sensitize the sequence to high gamma oscillations present in epileptogenic tissue. Phase cycling was applied to capture distributed current orientations. Voxel-wise subtraction of SL-off from SL-on images enabled the separation of T2* effects from rotary saturation effects. The topography of PC-SIRS effects was compared with the seizure onset zone at intracranial EEG and with surface IED-related potentials. Bayesian statistics were used to test whether prior PC-SIRS information could improve IED source reconstruction. Results Nonhemodynamic resonant saturation effects ipsilateral to the seizure onset zone were detected in six of eight patients (concordance rate, 0.75; 95% confidence interval: 0.40, 0.94) by means of the PC-SIRS technique. They were concordant with IED surface negativity in seven of eight patients (0.88; 95% confidence interval: 0.51, 1.00). Including PC-SIRS as prior information improved the evidence of the standard EEG source models compared with the use of uninformed reconstructions (exceedance probability, 0.77 vs 0.12; Wilcoxon test of model evidence, P < .05). Nonhemodynamic resonant saturation effects resolved in patients with favorable postsurgical outcomes, but persisted in patients with postsurgical seizure recurrence. Conclusion Nonhemodynamic resonant saturation effects are detectable during interictal periods with the PC-SIRS approach in patients with epilepsy. The method may be useful for MR imaging-based detection of neuronal currents in a clinical environment. (©) RSNA, 2016 Online supplemental material is available for this article.

Combined use of pulsed arterial spin-labeling and susceptibility-weighted imaging in stroke at 3T

Background and Purpose: In acute stroke it is no longer sufficient to detect simply ischemia, but also to try to evaluate reperfusion/recanalization status and predict eventual hemorrhagic transformation. Arterial spin labeling (ASL) perfusion may have advantages over contrast-enhanced perfusion-weighted imaging (cePWI), and susceptibility weighted imaging (SWI) has an intrinsic sensitivity to paramagnetic effects in addition to its ability to detect small areas of bleeding and hemorrhage. We want to determine here if their combined use in acute stroke and stroke follow-up at 3T could bring new insight into the diagnosis and prognosis of stroke leading to eventual improved patient management. Methods: We prospectively examined 41 patients admitted for acute stroke (NIHSS >1). Early imaging was performed between 1 h and 2 weeks. The imaging protocol included ASL, cePWI, SWI, T2 and diffusion tensor imaging (DTI), in addition to standard stroke protocol. Results: We saw four kinds of imaging patterns based on ASL and SWI: patients with either hypoperfusion and hyperperfusion on ASL with or without changes on SWI. Hyperperfusion was observed on ASL in 12/41 cases, with hyperperfusion status that was not evident on conventional cePWI images. Signs of hemorrhage or blood-brain barrier breakdown were visible on SWI in 15/41 cases, not always resulting in poor outcome (2/15 were scored mRS = 0–6). Early SWI changes, together with hypoperfusion, were associated with the occurrence of hemorrhage. Hyperperfusion on ASL, even when associated with hemorrhage detected on SWI, resulted in good outcome. Hyperperfusion predicted a better outcome than hypoperfusion (p = 0.0148). Conclusions: ASL is able to detect acute-stage hyperperfusion corresponding to luxury perfusion previously reported by PET studies. The presence of hyperperfusion on ASL-type perfusion seems indicative of reperfusion/collateral flow that is protective of hemorrhagic transformation and a marker of favorable tissue outcome. The combination of hypoperfusion and changes on SWI seems on the other hand to predict hemorrhage and/or poor outcome.

Theta burst TMS increases cerebral blood flow in the primary motor cortex during motor performance as assessed by arterial spin labeling (ASL)

Theta burst stimulation (TBS) is a novel variant of repetitive transcranial magnetic stimulation (rTMS), which induces changes in neuronal excitability persisting up to 1h. When elicited in the primary motor cortex, such physiological modulations might also have an impact on motor behavior. In the present study, we applied TBS in combination with pseudo continuous arterial spin labeling (pCASL) in order to address the question of whether TBS effects are measurable by means of changes in physiological parameters such as cerebral blood flow (CBF) and if TBS-induced plasticity can modify motor behavior. Twelve right-handed healthy subjects were stimulated using an inhibitory TBS protocol at subthreshold stimulation intensity targeted over the right motor cortex. The control condition consisted of within-subject Sham treatment in a crossover design. PCASL was performed before (pre TBS/pre Sham) and immediately after treatment (post TBS/post Sham). During the pCASL runs, the subjects performed a sequential fingertapping task with the left hand at individual maximum speed. There was a significant increase of CBF in the primary motor cortex after TBS, but not after Sham. It is assumed that inhibitory TBS induced a "local virtual lesion" which leads to the mobilization of more neuronal resources. There was no TBS-specific modulation in motor behavior, which might indicate that acute changes in brain plasticity caused by TBS are immediately compensated. This compensatory reaction seems to be observable at the metabolic, but not at the behavioral level.

Varying spin state composition by the choice of capping ligand in a family of molecular chains: detailed analysis of magnetic properties of chromium(III) horseshoes

We report a detailed physical analysis on a family of isolated, antiferro-magnetically (AF) coupled, chromium(III) finite chains, of general formula (Cr(RCO(2))(2)F)(n) where the chain length n = 6 or 7. Additionally, the chains are capped with a selection of possible terminating ligands, including hfac (= 1,1,1,5,5,5-hexafluoropentane-2,4-dionate(1-)), acac (= pentane-2,4-dionate(1-)) or (F)(3). Measurements by inelastic neutron scattering (INS), magnetometery and electron paramagnetic resonance (EPR) spectroscopy have been used to study how the electronic properties are affected by n and capping ligand type. These comparisons allowed the subtle electronic effects the choice of capping ligand makes for odd member spin 3/2 ground state and even membered spin 0 ground state chains to be investigated. For this investigation full characterisation of physical properties have been performed with spin Hamiltonian parameterisation, including the determination of Heisenberg exchange coupling constants and single ion axial and rhombic anisotropy. We reveal how the quantum spin energy levels of odd or even membered chains can be modified by the type of capping ligand terminating the chain. Choice of capping ligands enables Cr-Cr exchange coupling to be adjusted by 0, 4 or 24%, relative to Cr-Cr exchange coupling within the body of the chain, by the substitution of hfac, acac or (F)(3) capping ligands to the ends of the chain, respectively. The manipulation of quantum spin levels via ligands which play no role in super-exchange, is of general interest to the practise of spin Hamilton modelling, where such second order effects are generally not considered of relevance to magnetic properties.

Spin ladders and quantum simulators for Tomonaga–Luttinger liquids

Magnetic insulators have proven to be usable as quantum simulators for itinerant interacting quantum systems. In particular the compound (C5H12N)2CuBr4 (for short: (Hpip)2CuBr4) was shown to be a remarkable realization of a Tomonaga–Luttinger liquid (TLL) and allowed us to quantitatively test the TLL theory. Substitution weakly disorders this class of compounds and thus allows us to use them to tackle questions pertaining to the effect of disorder in TLL as well, such as that of the formation of the Bose glass. In this paper we present, as a first step in this direction, a study of the properties of the related (Hpip)2CuCl4 compound. We determine the exchange couplings and compute the temperature and magnetic field dependence of the specific heat, using a finite temperature density matrix renormalization group procedure. Comparison with the measured specific heat at zero magnetic field confirms the exchange parameters and Hamiltonian for the (Hpip)2CuCl4 compound, giving the basis needed to begin studying the disorder effects.

SALSA: a tool to estimate the stray light contamination for low-Earth orbit observatories

Stray light contamination reduces considerably the precision of photometric of faint stars for low altitude spaceborne observatories. When measuring faint objects, the necessity of coping with stray light contamination arises in order to avoid systematic impacts on low signal-to-noise images. Stray light contamination can be represented by a flat offset in CCD data. Mitigation techniques begin by a comprehensive study during the design phase, followed by the use of target pointing optimisation and post-processing methods. We present a code that aims at simulating the stray-light contamination in low-Earth orbit coming from reflexion of solar light by the Earth. StrAy Light SimulAtor (SALSA) is a tool intended to be used at an early stage as a tool to evaluate the effective visible region in the sky and, therefore to optimise the observation sequence. SALSA can compute Earth stray light contamination for significant periods of time allowing missionwide parameters to be optimised (e.g. impose constraints on the point source transmission function (PST) and/or on the altitude of the satellite). It can also be used to study the behaviour of the stray light at different seasons or latitudes. Given the position of the satellite with respect to the Earth and the Sun, SALSA computes the stray light at the entrance of the telescope following a geometrical technique. After characterising the illuminated region of the Earth, the portion of illuminated Earth that affects the satellite is calculated. Then, the flux of reflected solar photons is evaluated at the entrance of the telescope. Using the PST of the instrument, the final stray light contamination at the detector is calculated. The analysis tools include time series analysis of the contamination, evaluation of the sky coverage and an objects visibility predictor. Effects of the South Atlantic Anomaly and of any shutdown periods of the instrument can be added. Several designs or mission concepts can be easily tested and compared. The code is not thought as a stand-alone mission designer. Its mandatory inputs are a time series describing the trajectory of the satellite and the characteristics of the instrument. This software suite has been applied to the design and analysis of CHEOPS (CHaracterizing ExOPlanet Satellite). This mission requires very high precision photometry to detect very shallow transits of exoplanets. Different altitudes and characteristics of the detector have been studied in order to find the best parameters, that reduce the effect of contamination. © (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

CODE’s new solar radiation pressure model for GNSS orbit determination

The Empirical CODE Orbit Model (ECOM) of the Center for Orbit Determination in Europe (CODE), which was developed in the early 1990s, is widely used in the International GNSS Service (IGS) community. For a rather long time, spurious spectral lines are known to exist in geophysical parameters, in particular in the Earth Rotation Parameters (ERPs) and in the estimated geocenter coordinates, which could recently be attributed to the ECOM. These effects grew creepingly with the increasing influence of the GLONASS system in recent years in the CODE analysis, which is based on a rigorous combination of GPS and GLONASS since May 2003. In a first step we show that the problems associated with the ECOM are to the largest extent caused by the GLONASS, which was reaching full deployment by the end of 2011. GPS-only, GLONASS-only, and combined GPS/GLONASS solutions using the observations in the years 2009–2011 of a global network of 92 combined GPS/GLONASS receivers were analyzed for this purpose. In a second step we review direct solar radiation pressure (SRP) models for GNSS satellites. We demonstrate that only even-order short-period harmonic perturbations acting along the direction Sun-satellite occur for GPS and GLONASS satellites, and only odd-order perturbations acting along the direction perpendicular to both, the vector Sun-satellite and the spacecraft’s solar panel axis. Based on this insight we assess in the third step the performance of four candidate orbit models for the future ECOM. The geocenter coordinates, the ERP differences w. r. t. the IERS 08 C04 series of ERPs, the misclosures for the midnight epochs of the daily orbital arcs, and scale parameters of Helmert transformations for station coordinates serve as quality criteria. The old and updated ECOM are validated in addition with satellite laser ranging (SLR) observations and by comparing the orbits to those of the IGS and other analysis centers. Based on all tests, we present a new extended ECOM which substantially reduces the spurious signals in the geocenter coordinate z (by about a factor of 2–6), reduces the orbit misclosures at the day boundaries by about 10 %, slightly improves the consistency of the estimated ERPs with those of the IERS 08 C04 Earth rotation series, and substantially reduces the systematics in the SLR validation of the GNSS orbits.

Extraction of spin periods of space debris from optical light curves

The population of space debris increased drastically during the last years. These objects have become a great threat for active satellites. Because the relative velocities between space debris and satellites are high, space debris objects may destroy active satellites through collisions. Furthermore, collisions involving massive objects produce large number of fragments leading to significant growth of the space debris population. The long term evolution of the debris population is essentially driven by so-called catastrophic collisions. An effective remediation measure in order to stabilize the population in Low Earth Orbit (LEO) is therefore the removal of large, massive space debris. To remove these objects, not only precise orbits, but also more detailed information about their attitude states will be required. One important property of an object targeted for removal is its spin period, spin axis orientation and their change over time. Rotating objects will produce periodic brightness variations with frequencies which are related to the spin periods. Such a brightness variation over time is called a light curve. Collecting, but also processing light curves is challenging due to several reasons. Light curves may be undersampled, low frequency components due to phase angle and atmospheric extinction changes may be present, and beat frequencies may occur when the rotation period is close to a multiple of the sampling period. Depending on the method which is used to extract the frequencies, also method-specific properties have to be taken into account. The astronomical Institute of the University of Bern (AIUB) light curve database will be introduced, which contains more than 1,300 light curves acquired over more than seven years. We will discuss properties and reliability of different time series analysis methods tested and currently used by AIUB for the light curve processing. Extracted frequencies and reconstructed phases for some interesting targets, e.g. GLONASS satellites, for which also SLR data were available for the period confirmation, will be presented. Finally we will present the reconstructed phase and its evolution over time of a High-Area-to-Mass-Ratio (HAMR) object, which AIUB observed for several years.

Space debris attitude simulation - ιOTA (In-Orbit Tumbling Analysis)

Today, there is little knowledge on the attitude state of decommissioned intact objects in Earth orbit. Observational means have advanced in the past years, but are still limited with respect to an accurate estimate of motion vector orientations and magnitude. Especially for the preparation of Active Debris Removal (ADR) missions as planned by ESA’s Clean Space initiative or contingency scenarios for ESA spacecraft like ENVISAT, such knowledge is needed. ESA's “Debris Attitude Motion Measurements and Modelling” project (ESA Contract No. 40000112447), led by the Astronomical Institute of the University of Bern (AIUB), addresses this problem. The goal of the project is to achieve a good understanding of the attitude evolution and the considerable internal and external effects which occur. To characterize the attitude state of selected targets in LEO and GTO, multiple observation methods are combined. Optical observations are carried out by AIUB, Satellite Laser Ranging (SLR) is performed by the Space Research Institute of the Austrian Academy of Sciences (IWF) and radar measurements and signal level determination are provided by the Fraunhofer Institute for High Frequency Physics and Radar Techniques (FHR). The In-Orbit Tumbling Analysis tool (ιOTA) is a prototype software, currently in development by Hyperschall Technologie Göttingen GmbH (HTG) within the framework of the project. ιOTA will be a highly modular software tool to perform short-(days), medium-(months) and long-term (years) propagation of the orbit and attitude motion (six degrees-of-freedom) of spacecraft in Earth orbit. The simulation takes into account all relevant acting forces and torques, including aerodynamic drag, solar radiation pressure, gravitational influences of Earth, Sun and Moon, eddy current damping, impulse and momentum transfer from space debris or micro meteoroid impact, as well as the optional definition of particular spacecraft specific influences like tank sloshing, reaction wheel behaviour, magnetic torquer activity and thruster firing. The purpose of ιOTA is to provide high accuracy short-term simulations to support observers and potential ADR missions, as well as medium-and long-term simulations to study the significance of the particular internal and external influences on the attitude, especially damping factors and momentum transfer. The simulation will also enable the investigation of the altitude dependency of the particular external influences. ιOTA's post-processing modules will generate synthetic measurements for observers and for software validation. The validation of the software will be done by cross-calibration with observations and measurements acquired by the project partners.

Insolation, erosion, and morphology of comet 67P/Churyumov-Gerasimenko

Context. The complex shape of comet 67P and its oblique rotation axis cause pronounced seasonal effects. Irradiation and hence activity vary strongly. Aims. We investigate the insolation of the cometary surface in order to predict the sublimation of water ice. The strongly varying erosion levels are correlated with the topography and morphology of the present cometary surface and its evolution. Methods. The insolation as a function of heliocentric distance and diurnal (spin dependent) variation is calculated using >10(5) facets of a detailed digital terrain model. Shading, but also illumination and thermal radiation by facets in the field of view of a specific facet are iteratively taken into account. We use a two-layer model of a thin porous dust cover above an icy surface to calculate the water sublimation, presuming steady state and a uniform surface. Our second model, which includes the history of warming and cooling due to thermal inertia, is restricted to a much simpler shape model but allows us to test various distributions of active areas. Results. Sublimation from a dirty ice surface yields maximum erosion. A thin dust cover of 50 pm yields similar rates at perihelion. Only about 6% of the surface needs to be active to match the observed water production rates at perihelion. A dust layer of 1 mm thickness suppresses the activity by a factor of 4 to 5. Erosion on the south side can reach more than 10 m per orbit at active spots. The energy input to the concave neck area (Hapi) during northern summer is enhanced by about 50% owing to self-illumination. Here surface temperatures reach maximum values along the foot of the Hathor wall. Integrated over the whole orbit this area receives the least energy input. Based on the detailed shape model, the simulations identify "hot spots" in depressions and larger pits in good correlation with observed dust activity. Three-quarters of the total sublimation is produced while the sub-solar latitude is south, resulting in a distinct dichotomy in activity and morphology. Conclusions. The northern areas display a much rougher morphology than what is seen on Imhotep, an area at the equator that will be fully illuminated when 67P is closer to the Sun. Self-illumination in concave regions enhance the energy input and hence erosion. This explains the early activity observed at Hapi. Cliffs are more prone to erosion than horizontal, often dust covered, areas, which leads to surface planation. Local activity can only persist if the forming cliff walls are eroding. Comet 67P has two lobes and also two distinct sides. Transport of material from the south to the north is probable. The morphology of the Imhotep plain should be typical for the terrains of the yet unseen southern hemisphere.

Interstellar Flow and Temperature Determination with IBEX: Robustness and Sensitivity to Systematic Effects

The Interstellar Boundary Explorer (IBEX) samples the interstellar neutral (ISN) gas flow of several species every year from December through late March when the Earth moves into the incoming flow. The first quantitative analyses of these data resulted in a narrow tube in four-dimensional interstellar parameter space, which couples speed, flow latitude, flow longitude, and temperature, and center values with approximately 3° larger longitude and 3 km s⁻¹ lower speed, but with temperatures similar to those obtained from observations by the Ulysses spacecraft. IBEX has now recorded six years of ISN flow observations, providing a large database over increasing solar activity and using varying viewing strategies. In this paper, we evaluate systematic effects that are important for the ISN flow vector and temperature determination. We find that all models in use return ISN parameters well within the observational uncertainties and that the derived ISN flow direction is resilient against uncertainties in the ionization rate. We establish observationally an effective IBEX-Lo pointing uncertainty of ±0°18 in spin angle and confirm an uncertainty of ±0°1 in longitude. We also show that the IBEX viewing strategy with different spin-axis orientations minimizes the impact of several systematic uncertainties, and thus improves the robustness of the measurement. The Helium Warm Breeze has likely contributed substantially to the somewhat different center values of the ISN flow vector. By separating the flow vector and temperature determination, we can mitigate these effects on the analysis, which returns an ISN flow vector very close to the Ulysses results, but with a substantially higher temperature. Due to coupling with the ISN flow speed along the ISN parameter tube, we provide the temperature Tvisn∞=8710+440/-680 K for Visn∞=26 km s⁻¹ for comparison, where most of the uncertainty is systematic and likely due to the presence of the Warm Breeze.