6,713 research outputs found
Radial Velocity Confirmation of a Binary Detected from Pulse Timings
A periodic variation in the pulse timings of the pulsating hot subdwarf B
star CS 1246 was recently discovered via the O-C diagram and suggests the
presence of a binary companion with an orbital period of two weeks. Fits to
this phase variation, when interpreted as orbital reflex motion, imply CS 1246
orbits a barycenter 11 light-seconds away with a velocity of 16.6 km/s. Using
the Goodman spectrograph on the SOAR telescope, we decided to confirm this
hypothesis by obtaining radial velocity measurements of the system over several
months. Our spectra reveal a velocity variation with amplitude, period, and
phase in accordance with the O-C diagram predictions. This corroboration
demonstrates that the rapid pulsations of hot subdwarf B stars can be adequate
clocks for the discovery of binary companions via the pulse timing method.Comment: Accepted for publication in ApJ Letters; 5 pages, 2 figures, 3
tables; uses emulateap
Spin-Dependent Electron Transmission Model for Chiral Molecules in Mesoscopic Devices
Various device-based experiments have indicated that electron transfer in
certain chiral molecules may be spin-dependent, a phenomenon known as the
Chiral Induced Spin Selectivity (CISS) effect. However, due to the complexity
of these devices and a lack of theoretical understanding, it is not always
clear to what extent the chiral character of the molecules actually contributes
to the magnetic-field-dependent signals in these experiments. To address this
issue, we report here an electron transmission model that evaluates the role of
the CISS effect in two-terminal and multi-terminal linear-regime electron
transport experiments. Our model reveals that for the CISS effect, the
chirality-dependent spin transmission is accompanied by a spin-flip electron
reflection process. Furthermore, we show that more than two terminals are
required in order to probe the CISS effect in the linear regime. In addition,
we propose two types of multi-terminal nonlocal transport measurements that can
distinguish the CISS effect from other magnetic-field-dependent signals. Our
model provides an effective tool to review and design CISS-related transport
experiments, and to enlighten the mechanism of the CISS effect itself
Circuit-Model Analysis for Spintronic Devices with Chiral Molecules as Spin Injectors
Recent research discovered that charge transfer processes in chiral molecules
can be spin selective and named the effect chiral-induced spin selectivity
(CISS). Follow-up work studied hybrid spintronic devices with conventional
electronic materials and chiral (bio)molecules. However, a theoretical
foundation for the CISS effect is still in development and the spintronic
signals were not evaluated quantitatively. We present a circuit-model approach
that can provide quantitative evaluations. Our analysis assumes the scheme of a
recent experiment that used photosystem~I (PSI) as spin injectors, for which we
find that the experimentally observed signals are, under any reasonable
assumptions on relevant PSI time scales, too high to be fully due to the CISS
effect. We also show that the CISS effect can in principle be detected using
the same type of solid-state device, and by replacing silver with graphene, the
signals due to spin generation can be enlarged four orders of magnitude. Our
approach thus provides a generic framework for analyzing this type of
experiments and advancing the understanding of the CISS effect
24 \textmu m length spin relaxation length in boron nitride encapsulated bilayer graphene
We have performed spin and charge transport measurements in dual gated high
mobility bilayer graphene encapsulated in hexagonal boron nitride. Our results
show spin relaxation lengths up to 13~\textmu m at room temperature
with relaxation times of 2.5~ns. At 4~K, the diffusion coefficient
rises up to 0.52~m/s, a value 5 times higher than the best achieved for
graphene spin valves up to date. As a consequence, rises up to
24~\textmu m with as high as 2.9~ns. We characterized 3 different
samples and observed that the spin relaxation times increase with the device
length. We explain our results using a model that accounts for the spin
relaxation induced by the non-encapsulated outer regions.Comment: 5 pages and 4 figure
Separation of Racemic Mixtures of Amino Acids Using Chiral Eluents
A commercially available non-chiral RP-C8 chromatographic column is used with an aqueous chiral mobile phase containing N,N-dimethyl-L-phenylalanine and copper in a ratio 20 : 1 for the enantiomeric resolution of the following amino acids: DL-valine (Val), DL-methionine (Met), DL-leucine (Leu), DL-phenylalanine (Phe) and DL-tyrosine (Tyr). The influence of organic modifier, temperature and flow-rate on the capacity factors and on the selectivity is experimentally determined and the separation behavior is
discussed. The capacity factors of some of the amino acids remained constant with changing the composition of the mobile phase, i.e. increasing methanol amount. With increase of the temperature the retention times decreased and the selectivities were slightly
reduced. In a study of the effect on retention and selectivity, linear van’t Hoff plots were obtained giving ∆H and ∆S values of the solute transfer from the mobile to the stationary phase. These were found to be within the range obtained for hydrophobic compounds in RP-HPLC systems. Using van Deemter plots high separation efficiency and low apparent axial dispersion coefficients for all amino acids could be determined
Separation of Racemic Mixtures of Amino Acids Using Chiral Eluents
A commercially available non-chiral RP-C8 chromatographic column is used with an aqueous chiral mobile phase containing N,N-dimethyl-L-phenylalanine and copper in a ratio 20 : 1 for the enantiomeric resolution of the following amino acids: DL-valine (Val), DL-methionine (Met), DL-leucine (Leu), DL-phenylalanine (Phe) and DL-tyrosine (Tyr). The influence of organic modifier, temperature and flow-rate on the capacity factors and on the selectivity is experimentally determined and the separation behavior is
discussed. The capacity factors of some of the amino acids remained constant with changing the composition of the mobile phase, i.e. increasing methanol amount. With increase of the temperature the retention times decreased and the selectivities were slightly
reduced. In a study of the effect on retention and selectivity, linear van’t Hoff plots were obtained giving ∆H and ∆S values of the solute transfer from the mobile to the stationary phase. These were found to be within the range obtained for hydrophobic compounds in RP-HPLC systems. Using van Deemter plots high separation efficiency and low apparent axial dispersion coefficients for all amino acids could be determined
A model-based approach to stabilizing crutch supported paraplegic standing by artifical hip joint stiffness
The prerequisites for stable crutch supported standing were analyzed in this paper. For this purpose, a biomechanical model of crutch supported paraplegic stance was developed assuming the patient was standing with extended knees. When using crutches during stance, the crutches will put a position constraint on the shoulder, thus reducing the number of degrees of freedom. Additional hip-joint stiffness was applied to stabilize the hip joint and, therefore, to stabilize stance. The required hip-joint stiffness for changing crutch placement and hip-joint offset angle was studied under static and dynamic conditions. Modeling results indicate that, by using additional hip-joint stiffness, stable crutch supported paraplegic standing can be achieved, both under static as well as dynamic situations. The static equilibrium postures and the stability under perturbations were calculated to be dependent on crutch placement and stiffness applied. However, postures in which the hip joint was in extension (C postures) appeared to the most stable postures. Applying at least 60 N /spl middot/ m/rad hip-joint stiffness gave stable equilibrium postures in all cases. Choosing appropriate hip-joint offset angles, the static equilibrium postures changed to more erect postures, without causing instability or excessive arm forces to occur
Single-molecule real-time sequencing combined with optical mapping yields completely finished fungal genome
Next-generation sequencing (NGS) technologies have increased the scalability, speed, and resolution of genomic sequencing and, thus, have revolutionized genomic studies. However, eukaryotic genome sequencing initiatives typically yield considerably fragmented genome assemblies. Here, we assessed various state-of-the-art sequencing and assembly strategies in order to produce a contiguous and complete eukaryotic genome assembly, focusing on the filamentous fungus Verticillium dahliae. Compared with Illumina-based assemblies of the V. dahliae genome, hybrid assemblies that also include PacBio- generated long reads establish superior contiguity. Intriguingly, provided that sufficient sequence depth is reached, assemblies solely based on PacBio reads outperform hybrid assemblies and even result in fully assembled chromosomes. Furthermore, the addition of optical map data allowed us to produce a gapless and complete V. dahliae genome assembly of the expected eight chromosomes from telomere to telomere. Consequently, we can now study genomic regions that were previously not assembled or poorly assembled, including regions that are populated by repetitive sequences, such as transposons, allowing us to fully appreciate an organism’s biological complexity. Our data show that a combination of PacBio-generated long reads and optical mapping can be used to generate complete and gapless assemblies of fungal genomes. IMPORTANCE Studying whole-genome sequences has become an important aspect of biological research. The advent of nextgeneration sequencing (NGS) technologies has nowadays brought genomic science within reach of most research laboratories, including those that study nonmodel organisms. However, most genome sequencing initiatives typically yield (highly) fragmented genome assemblies. Nevertheless, considerable relevant information related to genome structure and evolution is likely hidden in those nonassembled regions. Here, we investigated a diverse set of strategies to obtain gapless genome assemblies, using the genome of a typical ascomycete fungus as the template. Eventually, we were able to show that a combination of PacBiogenerated long reads and optical mapping yields a gapless telomere-to-telomere genome assembly, allowing in-depth genome sanalyses to facilitate functional studies into an organism’s biology
- …