Spatial distribution of electric-field enhancement across the gap of terahertz bow-tie antennas

The electric-field enhancement in terahertz (THz) antennas designed for nonlinear THz spectroscopy of soft matter is characterized by spatially resolved electrooptic sampling. To mimic the relevant interaction geometry, metallic, resonant bow-tie antennas are deposited on a thin zinc telluride crystal of 10 µm thickness. The THz electric field transmitted through the antenna gap is recorded by electrooptic sampling. By focusing the 800 nm, sub-20 fs sampling pulses, we achieve a spatial resolution of some 3 µm, which is 1/3 to 1/8 of the antenna-gap width. The THz field in the gap displays an enhancement by a factor of up to 4.5 with a pronounced spectral variation, depending sensitively on the antenna-arm length and the gap width. By scanning the 800 nm probe spot laterally through the antenna gap, the spatial variation of the enhancement is determined, reaching the highest values at the edges of the gap. The results are in agreement with simulations of the electric-field distributions by finite-element calculations. © 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen

Relationships between greenhouse gas production and landscape position during short-term permafrost thaw under anaerobic conditions in the Lena Delta

Soils in the permafrost region have acted as car- bon sinks for thousands of years. As a result of global warming, permafrost soils are thawing and will potentially release greenhouse gases (GHGs) such as methane (CH4) and carbon dioxide (CO2). However, small-scale spatial heterogeneities of GHG production have been neglected in previous incubation studies. Here, we used an anaerobic incubation experiment to simulate permafrost thaw along a transect from upland Yedoma to the floodplain on Kurungnakh Island. Potential CO2 and CH4 production was measured during incubation of the active layer and permafrost soils at 4 and 20 ◦C, first for 60 d (approximate length of the growing season) and then continuing for 1 year. An assessment of methanogen abundance was performed in parallel for the first 60 d. Yedoma samples from upland and slope cores remained in a lag phase during the growing season simulation, while those located in the floodplain showed high production of CH4 (6.5 × 103 μg CH4-C g−1 C) and CO2 (6.9 × 103 μg CO2-C g−1 C) at 20 ◦C. The Yedoma samples from the permafrost layer started producing CH4 after 6 months of incubation. We conclude that landscape position is a key factor triggering CH4 production during the growing season time on Kurungnakh Island

Cerebrospinal fluid promotes survival and astroglial differentiation of adult human neural progenitor cells but inhibits proliferation and neuronal differentiation

<p>Abstract</p> <p>Background</p> <p>Neural stem cells (NSCs) are a promising source for cell replacement therapies for neurological diseases. Growing evidence suggests an important role of cerebrospinal fluid (CSF) not only on neuroectodermal cells during brain development but also on the survival, proliferation and fate specification of NSCs in the adult brain. Existing <it>in vitro </it>studies focused on embryonic cell lines and embryonic CSF. We therefore studied the effects of adult human leptomeningeal CSF on the behaviour of adult human NSCs (ahNSCs).</p> <p>Results</p> <p>Adult CSF increased the survival rate of adult human NSCs compared to standard serum free culture media during both stem cell maintenance and differentiation. The presence of CSF promoted differentiation of NSCs leading to a faster loss of their self-renewal capacity as it is measured by the proliferation markers Ki67 and BrdU and stronger cell extension outgrowth with longer and more cell extensions per cell. After differentiation in CSF, we found a larger number of GFAP⁺astroglial cells compared to differentiation in standard culture media and a lower number of β-tubulin III⁺neuronal cells.</p> <p>Conclusions</p> <p>Our data demonstrate that adult human leptomeningeal CSF creates a beneficial environment for the survival and differentiation of adult human NSCs. Adult CSF is <it>in vitro </it>a strong glial differentiation stimulus and leads to a rapid loss of stem cell potential.</p

Impact of Rotational Twin Boundaries and Lattice Mismatch on III-V Nanowire Growth

Pseudomorphic planar III-V transition layers greatly facilitate the epitaxial integration of vapor liquid solid grown III-V nanowires (NW) on Si(111) substrates. Heteroepitaxial (111) layer growth, however, is commonly accompanied by the formation of rotational twins. We find that rotational twin boundaries (RTBs), which intersect the surface of GaP/Si(111) heterosubstrates, generally cause horizontal NW growth and may even suppress NW growth entirely. Away from RTBs, the NW growth direction switches from horizontal to vertical in the case of homoepitaxial GaP NWs, whereas heteroepitaxial GaAs NWs continue growing horizontally. To understand this rich phenomenology, we develop a model based on classical nucleation theory. Independent of the occurrence of RTBs and specific transition layers, our model can generally explain the prevalent observation of horizontal III V NW growth-in lattice mismatched systems and the high crystal quality of horizontal nanowires.This work was financially supported by the BMBF (Project No. 03SF0404A) and partly by the Spanish Ministry of Economy (Project TEC2014-54260-C3-2-P). C.K. and L.W. acknowledge the Thuringia Graduate School for Photovoltaics “Photograd” for financial support. The authors would like to thank A. Paszuk and A. Nagelein for valuable discussions as well as A. Muller and M. Biester for technical support, T. Nieszner for supporting the determination of the spatial direction of NWs, and D. Roßberg for preparing the TEM lamella

Cord Blood Vα24-Vβ11+ Natural Killer T Cells Display a Th2-Chemokine Receptor Profile and Cytokine Responses

Background: The fetal immune system is characterized by a Th2 bias but it is unclear how the Th2 predominance is established. Natural killer T (NKT) cells are a rare subset of T cells with immune regulatory functions and are already activated in utero. To test the hypothesis that NKT cells are part of the regulatory network that sets the fetal Th2 predominance, percentages of Vα24(+)Vβ11(+) NKT cells expressing Th1/Th2-related chemokine receptors (CKR) were assessed in cord blood. Furthermore, IL-4 and IFN-γ secreting NKT cells were quantified within the single CKR(+) subsets. Results: Cord blood NKT cells expressed the Th2-related CCR4 and CCR8 at significantly higher frequencies compared to peripheral blood NKT cells from adults, while CXCR3+ and CCR5+ cord blood NKT cells (Th1-related) were present at lower percentages. Within CD4negCD8neg (DN) NKT cells, the frequency of IL-4 producing NKT cells was significantly higher in cord blood, while frequencies of IFN-γ secreting DN NKT cells tended to be lower. A further subanalysis showed that the higher percentage of IL-4 secreting DN NKT cells was restricted to CCR3+, CCR4+, CCR5+, CCR6+, CCR7+, CCR8+ and CXCR4+ DN subsets in cord blood. This resulted in significantly decreased IFN-γ /IL-4 ratios of CCR3+, CCR6+ and CCR8+ cord blood DN NKT cells. Sequencing of VA24AJ18 T cell receptor (TCR) transcripts in sorted cord blood Vα24Vβ11 cells confirmed the invariant TCR alpha-chain ruling out the possibility that these cells represent an unusual subset of conventional T cells. Conclusions: Despite the heterogeneity of cord blood NKT cells, we observed a clear Th2-bias at the phenotypic and functional level which was mainly found in the DN subset. Therefore, we speculate that NKT cells are important for the initiation and control of the fetal Th2 environment which is needed to maintain tolerance towards self-antigens as well as non-inherited maternal antigens

Thermodynamics of Random Ferromagnetic Antiferromagnetic Spin-1/2 Chains

Using the quantum Monte Carlo Loop algorithm, we calculate the temperature dependence of the uniform susceptibility, the specific heat, the correlation length, the generalized staggered susceptibility and magnetization of a spin-1/2 chain with random antiferromagnetic and ferromagnetic couplings, down to very low temperatures. Our data show a consistent scaling behavior in all the quantities and support strongly the conjecture drawn from the approximate real-space renormalization group treatment.A statistical analysis scheme is developed which will be useful for the search of scaling behavior in numerical and experimental data of random spin chains.Comment: 13 pages, 13 figures, RevTe

The Anderson Model out of equilibrium: Time dependent perturbations

The influence of high-frequency fields on quantum transport through a quantum dot is studied in the low-temperature regime. We generalize the non crossing approximation for the infinite-U Anderson model to the time-dependent case. The dc spectral density shows asymmetric Kondo side peaks due to photon-assisted resonant tunneling. As a consequence we predict an electron-photon pump at zero bias which is purely based on the Kondo effect. In contrast to the resonant level model and the time-independent case we observe asymmetric peak amplitudes in the Coulomb oscillations and the differential conductance versus bias voltage shows resonant side peaks with a width much smaller than the tunneling rate. All the effects might be used to clarify the question whether quantum dots indeed show the Kondo effect.Comment: 13 pages, REVTEX 3.0, 5 figure

Juvenile Myoclonic Epilepsy Shows Potential Structural White Matter Abnormalities: A TBSS Study

Background: Several studies on patients with juvenile myoclonic epilepsy (JME) showed widespread white matter (WM) abnormalities in the brain. The aim of this study was to investigate potential structural abnormalities in JME patients (1) compared to healthy controls, (2) among JME subgroups with or without photoparoxysmal responses (PPR), and (3) in correlation with clinical variables.Methods: A selection of 31 patients with JME (12 PPR positive) and 27 age and gender matched healthy controls (HC) were studied at a tertiary epilepsy center. Fractional anisotropy (FA) was calculated and intergroup differences analyzed using Tract Based Spatial Statistics (TBSS).Results: Compared to HC the JME group showed reduced FA widespread and bilateral in the longitudinal fasciculus, inferior fronto-occipital fasciculus, corticospinal tract, anterior and posterior thalamic radiation, corona radiata, corpus callosum, cingulate gyrus and external capsule (p &lt; 0.01). Subgroup analysis revealed no significant differences of WM alterations between PPR positive and negative patients and with clinical and epilepsy-related factors.Conclusions: Widespread microstructural abnormalities among patients with JME have been identified.Prior findings of frontal and thalamofrontal microstructural abnormalities have been confirmed. Additionally, microstructural abnormalities were found in widespread extra-frontal regions that may help to validate pathophysiological concepts of JME

Remote sensing of drained thermokarst lake basin successions

Thermokarst lakes are important factors for permafrost landscape dynamics and carbon cycling. Thermokarst lake cover is particularly high in Arctic lowlands with ice-rich permafrost. In many of these vast lowland regions, drained thermokarst lake basins of different age have been identified that overlap each other in space, suggesting intense dynamics of repeated lake formation and loss with complex carbon cycle histories during the Holocene [Grosse et al.,2013]. Observing the permafrost and ecosystem succession patterns following thermokarst lake drainage will help to better determining the landscape and regional scale impacts of lake loss on northern hydrology, permafrost aggradation, vegetation succession, carbon cycling, as well as spectral land surface property changes. Previous remote sensing approaches to study drained thermokarst lake basins used a combination of Landsat, high resolution satellite and aerial, and field data to quantify carbon stocks accumulated in post-drainage peat in drained thermokarst lake basins (DTLBs) for the northern Seward Peninsula in Northwest Alaska [Jones et al., 2012]. We here expand on this method by using different remote sensing products in combination with dating of lake drainage events. These events are identified based on the historical remote sensing record and accelerated mass spectrometry radiocarbon dating. The joint us of remote sensing and geochronological field data allows to assess the specific succession patterns of various DTLB types and their impacts on land surface properties in different Arctic permafrost regions (North Alaska, Northwest Alaska, North Siberia). The datasets used in this analysis include a range of remote sensing and topographic data, such as aerial photography, historic topographic maps, high resolution satellite images (Corona, Spot, Ikonos, Quickbird, Worldview, GeoEye), and imagery from the full Landsat archive as well as from the Moderate Resolution Imaging Spectrometer (MODIS) sensors. We report temporal trends of spectral properties based on Landsat multispectral indices for individual DTLBs of different ages, but also employ landscape-scale chronosequences allowing the analysis succession trajectories of DTLBs that drained well before the start of the remote sensing record. Here we are particularly focusing on the long-term impacts of lake drainage on changes in normalized difference vegetation index (NDVI), normalized difference moisture index (NDMI), normalized difference water index (NDWI), Tasseled Cap index (brightness, greenness, wetness), land surface temperatures, and albedo. We further conducted field studies including reconnaissance flights targeting historically drained lakes and cored DTLBs to sample for radiocarbon-dating of terrestrial peat layers indicative of the drainage event. Results of this ongoing study suggest a strong impact exerted by thermokarst lake drainage on land surface reflectance characteristics in thermokarst lowland regions. The information may be useful for parameterizing surface properties in land surface models of thermokarst-affected regions, particularly where increased lake drainage is projected to take place