427 research outputs found
Slow light with a swept-frequency source
We introduce a new concept for stimulated-Brillouin-scattering-based slow
light in optical fibers that is applicable for broadly-tunable frequency-swept
sources. It allows slow light to be achieved, in principle, over the entire
transparency window of the optical fiber. We demonstrate a slow light delay of
10 ns at 1550 nm using a 10-m-long photonic crystal fiber with a source sweep
rate of 0.4 MHz/ns and a pump power of 200 mW. We also show that there exists a
maximal delay obtainable by this method, which is set by the SBS threshold,
independent of sweep rate. For our fiber with optimum length, this maximum
delay is ~38 ns, obtained for a pump power of 760 mW.Comment: 6 pages, 5 figure
BOC is a modifier gene in holoprosencephaly
Holoprosencephaly (HPE), a common developmental defect of the forebrain and midface, has a complex etiology. Heterozygous, loss‐of‐function mutations in the sonic hedgehog (SHH) pathway are associated with HPE. However, mutation carriers display highly variable clinical presentation, leading to an “autosomal dominant with modifier” model, in which the penetrance and expressivity of a predisposing mutation is graded by genetic or environmental modifiers. Such modifiers have not been identified. Boc encodes a SHH coreceptor and is a silent HPE modifier gene in mice. Here, we report the identification of missense BOC variants in HPE patients. Consistent with these alleles functioning as HPE modifiers, individual variant BOC proteins had either loss‐ or gain‐of‐function properties in cell‐based SHH signaling assays. Therefore, in addition to heterozygous loss‐of‐function mutations in specific SHH pathway genes and an ill‐defined environmental component, our findings identify a third variable in HPE: low‐frequency modifier genes, BOC being the first identified.Holoprosencephaly (HPE), the most developmental common defect of the forebrain, is best explained by a “mutation with modifier” model. However, HPE modifier genes have not been identified. Here, we report HPE‐associated missense variants within the Hedgehog coreceptor BOC (arrows). Functional analyses of these variants, along with previous work in mouse models, are consistent with the conclusion that these variants act as phenotypic modifiers of a driver mutation or environmental insult.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138902/1/humu23286-sup-0001-text.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/138902/2/humu23286_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/138902/3/humu23286.pd
Electron Angular Distributions in He Single Ionization Impact by H₂⁺ Ions at 1 MeV
For the first time we investigated in a kinematically complete experiment the ionization of helium in collisions with H2+-molecular ions at 1 MeV. Using two separate detectors, the orientation of the projectile H2+-molecular ions was determined at the instance of the collision. The electron angular distribution was measured by a Reaction Microscope . The observed structures are found in agreement with theoretical calculations, indicating that the ionized electron of He shows a slight preferential emission direction parallel to the molecular axis
Understanding the impact of heavy ions and tailoring the optical properties of large-area Monolayer WS2 using Focused Ion Beam
Focused ion beam (FIB) has been used as an effective tool for precise
nanoscale fabrication. It has recently been employed to tailor defect
engineering in functional nanomaterials such as two-dimensional transition
metal dichalcogenides (TMDCs), providing desirable properties in TMDC-based
optoelectronic devices. However, the damage caused by the FIB irradiation and
milling process to these delicate atomically thin materials, especially in the
extended area, has not yet been elaboratively characterised. Understanding the
correlation between lateral ion beam effects and optical properties of 2D TMDCs
is crucial in designing and fabricating high-performance optoelectronic
devices. In this work, we investigate lateral damage in large-area monolayer
WS2 caused by the gallium focused ion beam milling process. Three distinct
zones away from the milling location are identified and characterised via
steady-state photoluminescence (PL) and Raman spectroscopy. An unexpected
bright ring-shaped emission around the milled location has been revealed by
time-resolved PL spectroscopy with high spatial resolution. Our finding opens
new avenues for tailoring the optical properties of TMDCs by charge and defect
engineering via focused ion beam lithography. Furthermore, our study provides
evidence that while some localised damage is inevitable, distant destruction
can be eliminated by reducing the ion beam current. It paves the way for the
use of FIB to create nanostructures in 2D TMDCs, as well as the design and
realisation of optoelectrical devices on a wafer scale
CMBPol Mission Concept Study: Prospects for polarized foreground removal
In this report we discuss the impact of polarized foregrounds on a future
CMBPol satellite mission. We review our current knowledge of Galactic polarized
emission at microwave frequencies, including synchrotron and thermal dust
emission. We use existing data and our understanding of the physical behavior
of the sources of foreground emission to generate sky templates, and start to
assess how well primordial gravitational wave signals can be separated from
foreground contaminants for a CMBPol mission. At the estimated foreground
minimum of ~100 GHz, the polarized foregrounds are expected to be lower than a
primordial polarization signal with tensor-to-scalar ratio r=0.01, in a small
patch (~1%) of the sky known to have low Galactic emission. Over 75% of the sky
we expect the foreground amplitude to exceed the primordial signal by about a
factor of eight at the foreground minimum and on scales of two degrees. Only on
the largest scales does the polarized foreground amplitude exceed the
primordial signal by a larger factor of about 20. The prospects for detecting
an r=0.01 signal including degree-scale measurements appear promising, with 5
sigma_r ~0.003 forecast from multiple methods. A mission that observes a range
of scales offers better prospects from the foregrounds perspective than one
targeting only the lowest few multipoles. We begin to explore how optimizing
the composition of frequency channels in the focal plane can maximize our
ability to perform component separation, with a range of typically 40 < nu <
300 GHz preferred for ten channels. Foreground cleaning methods are already in
place to tackle a CMBPol mission data set, and further investigation of the
optimization and detectability of the primordial signal will be useful for
mission design.Comment: 42 pages, 14 figures, Foreground Removal Working Group contribution
to the CMBPol Mission Concept Study, v2, matches AIP versio
Metasurface-enhanced Mid-infrared Spectroscopy in the Liquid Phase
Vibrational spectroscopy is an important tool in chemical and biological analysis. A key issue when applying vibrational spectroscopy to dilute liquid samples is the inherently low sensitivity caused by short interaction lengths and small extinction coefficients, combined with low target molecule concentrations. Here, we introduce a novel type of surface-enhanced infrared absorption spectroscopy based on the resonance of a dielectric metasurface. We demonstrate that the method is suitable for probing vibrational bands of dilute analytes with a range of spectral linewidths. We observe that the absorption signal is enhanced by 1–2 orders of magnitude and show that this enhancement leads to a lower limit of detection compared to attenuated total reflection (ATR). Overall, the technique provides an important addition to the spectroscopist's toolkit especially for probing dilute samples
Les Houches 2013: Physics at TeV Colliders: Standard Model Working Group Report
This Report summarizes the proceedings of the 2013 Les Houches workshop on
Physics at TeV Colliders. Session 1 dealt primarily with (1) the techniques for
calculating standard model multi-leg NLO and NNLO QCD and NLO EW cross sections
and (2) the comparison of those cross sections with LHC data from Run 1, and
projections for future measurements in Run 2.Comment: Proceedings of the Standard Model Working Group of the 2013 Les
Houches Workshop, Physics at TeV Colliders, Les houches 3-21 June 2013. 200
page
CMBPol Mission Concept Study: Probing Inflation with CMB Polarization
We summarize the utility of precise cosmic microwave background (CMB)
polarization measurements as probes of the physics of inflation. We focus on
the prospects for using CMB measurements to differentiate various inflationary
mechanisms. In particular, a detection of primordial B-mode polarization would
demonstrate that inflation occurred at a very high energy scale, and that the
inflaton traversed a super-Planckian distance in field space. We explain how
such a detection or constraint would illuminate aspects of physics at the
Planck scale. Moreover, CMB measurements can constrain the scale-dependence and
non-Gaussianity of the primordial fluctuations and limit the possibility of a
significant isocurvature contribution. Each such limit provides crucial
information on the underlying inflationary dynamics. Finally, we quantify these
considerations by presenting forecasts for the sensitivities of a future
satellite experiment to the inflationary parameters.Comment: 107 pages, 14 figures, 17 tables; Inflation Working Group
contribution to the CMBPol Mission Concept Study; v2: typos fixed and
references adde
Rapid, ultra low coverage copy number profiling of cell-free DNA as a precision oncology screening strategy.
Current cell-free DNA (cfDNA) next generation sequencing (NGS) precision oncology workflows are typically limited to targeted and/or disease-specific applications. In advanced cancer, disease burden and cfDNA tumor content are often elevated, yielding unique precision oncology opportunities. We sought to demonstrate the utility of a pan-cancer, rapid, inexpensive, whole genome NGS of cfDNA approach (PRINCe) as a precision oncology screening strategy via ultra-low coverage (~0.01x) tumor content determination through genome-wide copy number alteration (CNA) profiling. We applied PRINCe to a retrospective cohort of 124 cfDNA samples from 100 patients with advanced cancers, including 76 men with metastatic castration-resistant prostate cancer (mCRPC), enabling cfDNA tumor content approximation and actionable focal CNA detection, while facilitating concordance analyses between cfDNA and tissue-based NGS profiles and assessment of cfDNA alteration associations with mCRPC treatment outcomes. Therapeutically relevant focal CNAs were present in 42 (34%) cfDNA samples, including 36 of 93 (39%) mCRPC patient samples harboring AR amplification. PRINCe identified pre-treatment cfDNA CNA profiles facilitating disease monitoring. Combining PRINCe with routine targeted NGS of cfDNA enabled mutation and CNA assessment with coverages tuned to cfDNA tumor content. In mCRPC, genome-wide PRINCe cfDNA and matched tissue CNA profiles showed high concordance (median Pearson correlation = 0.87), and PRINCe detectable AR amplifications predicted reduced time on therapy, independent of therapy type (Kaplan-Meier log-rank test, chi-square = 24.9, p < 0.0001). Our screening approach enables robust, broadly applicable cfDNA-based precision oncology for patients with advanced cancer through scalable identification of therapeutically relevant CNAs and pre-/post-treatment genomic profiles, enabling cfDNA- or tissue-based precision oncology workflow optimization
A global biophysical typology of mangroves and its relevance for ecosystem structure and deforestation
Mangrove forests provide many ecosystem services but are among the world's most threatened ecosystems. Mangroves vary substantially according to their geomorphic and sedimentary setting; while several conceptual frameworks describe these settings, their spatial distribution has not been quantified. Here, we present a new global mangrove biophysical typology and show that, based on their 2016 extent, 40.5% (54,972 km2) of mangrove systems were deltaic, 27.5% (37,411 km2) were estuarine and 21.0% (28,493 km2) were open coast, with lagoonal mangroves the least abundant (11.0%, 14,993 km2). Mangroves were also classified based on their sedimentary setting, with carbonate mangroves being less abundant than terrigenous, representing just 9.6% of global coverage. Our typology provides a basis for future research to incorporate geomorphic and sedimentary setting in analyses. We present two examples of such applications. Firstly, based on change in extent between 1996 and 2016, we show while all types exhibited considerable declines in area, losses of lagoonal mangroves (- 6.9%) were nearly twice that of other types. Secondly, we quantify differences in aboveground biomass between mangroves of different types, with it being significantly lower in lagoonal mangroves. Overall, our biophysical typology provides a baseline for assessing restoration potential and for quantifying mangrove ecosystem service provision
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