224 research outputs found
Sub-milliKelvin spatial thermometry of a single Doppler cooled ion in a Paul trap
We report on observations of thermal motion of a single, Doppler-cooled ion
along the axis of a linear radio-frequency quadrupole trap. We show that for a
harmonic potential the thermal occupation of energy levels leads to Gaussian
distribution of the ion's axial position. The dependence of the spatial thermal
spread on the trap potential is used for precise calibration of our imaging
system's point spread function and sub-milliKelvin thermometry. We employ this
technique to investigate the laser detuning dependence of the Doppler
temperature.Comment: 5 pages, 4 figure
Insect resistance of a full sib family of tetraploid switchgrass \u3ci\u3ePanicum virgatum\u3c/i\u3e L. with varying lignin levels
Little information is available on insect resistance mechanisms and inheritance in biomass grasses. Although reduction of lignin in biomass grasses in order to increase the efficiency of fermentation may result in increased susceptibility to insect feeding, other resistance mechanisms may be more important. Field grown leaves of two tetraploid parent (Kanlow N1, Summer) and 14 progeny switchgrass (Panicum virgatum L.) plant clones selected for a diversity of plant form and ranges in lignin levels were tested for leaf resistance to feeding by the fall armyworm (Spodoptera frugiperda J. E. Smith), a grass feeding insect pest. Although lignin generally appeared important as a resistance mechanism only at early season stages, replicate clones of two low lignin progeny plants generally remained resistant to fall armyworm feeding. Mechanical damaging increased resistance to fall armyworm feeding in several of these plants. Degrees of resistance were sometimes associated with leaf form of progeny. These results indicate there are likely multiple insect resistance mechanisms operating at different stages in switchgrass, and that segregation of some mechanisms appears related to growth form of the plants
In non-transformed cells Bak activates upon loss of anti-apoptotic Bcl-X-L and Mcl-1 but in the absence of active BH3-only proteins
Mitochondrial apoptosis is controlled by proteins of the B-cell lymphoma 2 (Bcl-2) family. Pro-apoptotic members of this family, known as BH3-only proteins, initiate activation of the effectors Bcl-2-associated X protein (Bax) and Bcl-2 homologous antagonist/killer (Bak),which is counteracted by anti-apoptotic family members. How the interactions of Bcl-2 proteins regulate cell death is still not entirely clear. Here, we show that in the absence of extrinsic apoptotic stimuli Bak activates without detectable contribution from BH3-only proteins, and cell survival depends on anti-apoptotic Bcl-2 molecules. All anti-apoptotic Bcl-2 proteins were targeted via RNA interference alone or in combinations of two in primary human fibroblasts. Simultaneous targeting of B-cell lymphoma-extra large and myeloid cell leukemia sequence 1 led to apoptosis in several cell types. Apoptosis depended on Bak whereas Bax was dispensable. Activator BH3-only proteins were not required for apoptosis induction as apoptosis was unaltered in the absence of all BH3-only proteins known to activate Bax or Bak directly, Bcl-2-interacting mediator of cell death, BH3-interacting domain death agonist and p53-upregulated modulator of apoptosis. These findings argue for auto-activation of Bak in the absence of anti-apoptotic Bcl-2 proteins and provide evidence of profound differences in the activation of Bax and Bak
In non-transformed cells Bak activates upon loss of anti-apoptotic Bcl-X-L and Mcl-1 but in the absence of active BH3-only proteins
Mitochondrial apoptosis is controlled by proteins of the B-cell lymphoma 2 (Bcl-2) family. Pro-apoptotic members of this family, known as BH3-only proteins, initiate activation of the effectors Bcl-2-associated X protein (Bax) and Bcl-2 homologous antagonist/killer (Bak),which is counteracted by anti-apoptotic family members. How the interactions of Bcl-2 proteins regulate cell death is still not entirely clear. Here, we show that in the absence of extrinsic apoptotic stimuli Bak activates without detectable contribution from BH3-only proteins, and cell survival depends on anti-apoptotic Bcl-2 molecules. All anti-apoptotic Bcl-2 proteins were targeted via RNA interference alone or in combinations of two in primary human fibroblasts. Simultaneous targeting of B-cell lymphoma-extra large and myeloid cell leukemia sequence 1 led to apoptosis in several cell types. Apoptosis depended on Bak whereas Bax was dispensable. Activator BH3-only proteins were not required for apoptosis induction as apoptosis was unaltered in the absence of all BH3-only proteins known to activate Bax or Bak directly, Bcl-2-interacting mediator of cell death, BH3-interacting domain death agonist and p53-upregulated modulator of apoptosis. These findings argue for auto-activation of Bak in the absence of anti-apoptotic Bcl-2 proteins and provide evidence of profound differences in the activation of Bax and Bak
Beam pattern evolution of accreting X-ray pulsar 1A 0535+262 during its 2020 giant outburst
We report on pulse profile decomposition analysis of a bright transient X-ray
pulsar 1A 0535+262 using the broadband Insight-HXMT observations during a giant
outburst of the source in 2020. We show that the observed pulse profile shape
can be described in terms of a combination of two symmetric single-pole
contributions for wide range of energies and luminosities for a fixed geometry
defining basic geometry of the pulsar. This corresponds to a slightly distorted
dipole magnetic field, i.e., one pole has to be offset by
from the antipodal position of the other pole. We reconstruct the intrinsic
beam patterns of the pulsar assuming the geometry recovered from the
decomposition analysis, and find evidence for a transition between "pencil" and
"fan" beams in energy ranges above the cyclotron line energy which can be
interpreted as transition from sub- to super-critical accretion regimes
associated with onset of an accretion column. At lower energies the beam
pattern appears, however, to be more complex, and contains substantial "fan"
beam and an additional "pencil" beam component at all luminosities. The latter
is not related to the accretion rate and is stronger in the fading phase of the
outburst. We finally discuss results in context of other observational and
theoretical findings earlier reported for the source in the literature.Comment: 14 pages, 8 figures. Accepted by Ap
Sources of organic gases and aerosol particles and their roles in nighttime particle growth at a rural forested site in southwest Germany
The composition, sources and chemical transformation of volatile organic compounds (VOCs) and organic aerosol (OA) particles were investigated during July–August 2021 at a rural forested site in southwest Germany, 10 km north of the city of Karlsruhe. VOCs and semi-volatile OA particles were measured with a proton-transfer-reaction mass spectrometer coupled to the CHemical Analysis of aeRosols ONline particle inlet (CHARON–PTR-MS). The CHARON-measured OA mass accounted for 62 ± 18 % on average of the total OA mass (4.2 ± 2.8 µg m−3) measured concurrently with an aerosol mass spectrometer (AMS). The total concentrations of measured VOCs ranged from 7.6 to 88.9 ppb with an average of 31.2 ± 13.4 ppb. Positive matrix factorization (PMF) was used to identify major source factors of VOCs and OA particles. Three types of oxygenated VOC (OVOC), namely aromatic OVOCs, biogenic OVOCs and aged OVOCs, contributed on average 11 % ± 9 %, 37 % ± 29 % and 29 % ± 21 % of total VOC concentrations, respectively. The results of AMS–PMF indicated substantial contributions of oxygenated organic compounds to OA particle mass. Three secondary OA (SOA) factors determined by CHARON–PMF analysis, namely aromatic SOA (5 % ± 7 %), daytime biogenic SOA (17 % ± 17 %) and nighttime biogenic SOA (28 % ± 21 %), consistently showed high contributions to the total CHARON-measured OA mass. Nighttime particle growth was observed regularly in this area, which was mainly attributed to the semi-volatile organic compounds and organic nitrates formed from the oxidation of monoterpenes and sesquiterpenes. This study presents the major sources, real-time transformations of VOCs and OA particles, and nighttime particle formation characteristics for central European forested areas.</p
Selective scattering between Floquet-Bloch and Volkov states in a topological insulator
The coherent optical manipulation of solids is emerging as a promising way to
engineer novel quantum states of matter. The strong time periodic potential of
intense laser light can be used to generate hybrid photon-electron states.
Interaction of light with Bloch states leads to Floquet-Bloch states which are
essential in realizing new photo-induced quantum phases. Similarly, dressing of
free electron states near the surface of a solid generates Volkov states which
are used to study non-linear optics in atoms and semiconductors. The
interaction of these two dynamic states with each other remains an open
experimental problem. Here we use Time and Angle Resolved Photoemission
Spectroscopy (Tr-ARPES) to selectively study the transition between these two
states on the surface of the topological insulator Bi2Se3. We find that the
coupling between the two strongly depends on the electron momentum, providing a
route to enhance or inhibit it. Moreover, by controlling the light polarization
we can negate Volkov states in order to generate pure Floquet-Bloch states.
This work establishes a systematic path for the coherent manipulation of solids
via light-matter interaction.Comment: 21 pages, 6 figures, final version to appear in Nature Physic
Recent Experimental Tests of Special Relativity
We review our recent Michelson-Morley (MM) and Kennedy-Thorndike (KT)
experiment, which tests Lorentz invariance in the photon sector, and report
first results of our ongoing atomic clock test of Lorentz invariance in the
matter sector. The MM-KT experiment compares a cryogenic microwave resonator to
a hydrogen maser, and has set the most stringent limit on a number of
parameters in alternative theories to special relativity. We also report first
results of a test of Lorentz invariance in the SME (Standard Model Extension)
matter sector, using Zeeman transitions in a laser cooled Cs atomic fountain
clock. We describe the experiment together with the theoretical model and
analysis. Recent experimental results are presented and we give a first
estimate of components of the parameters of the SME matter
sector. A full analysis of systematic effects is still in progress, and will be
the subject of a future publication together with our final results. If
confirmed, the present limits would correspond to first ever measurements of
some components, and improvements by 11 and 14 orders of
magnitude on others.Comment: 29 pages. Contribution to Springer Lecture Notes, "Special Relativity
- Will it survive the next 100 years ?", Proceedings, Potsdam, 200
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Effects of Odd–Even Side Chain Length of Alkyl-Substituted Diphenylbithiophenes on First Monolayer Thin Film Packing Structure
Because of their preferential two-dimensional layer-by-layer growth in thin films, 5,5′bis(4-alkylphenyl)-2,2′-bithiophenes (P2TPs) are model compounds for studying the effects of systematic chemical structure variations on thin-film structure and morphology, which in turn, impact the charge transport in organic field-effect transistors. For the first time, we observed, by grazing incidence X-ray diffraction (GIXD), a strong change in molecular tilt angle in a monolayer of P2TP, depending on whether the alkyl chain on the P2TP molecules was of odd or even length. The monolayers were deposited on densely packed ultrasmooth self-assembled alkane silane modified surfaces. Our work shows that a subtle change in molecular structure can have a significant impact on the molecular packing structure in thin film, which in turn, will have a strong impact on charge transport of organic semiconductors. This was verified by quantum-chemical calculations that predict a corresponding odd–even effect in the strength of the intermolecular electronic coupling.Chemistry and Chemical BiologyEngineering and Applied Science
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