665 research outputs found
Emergent Lorentz symmetry with vanishing velocity in a critical two-subband quantum wire
We consider a quantum wire with two subbands of spin-polarized electrons in
the presence of strong interactions. We focus on the quantum phase transition
when the second subband starts to get filled as a function of gate voltage.
Performing a one-loop renormalization group (RG) analysis of the effective
Hamiltonian, we identify the critical fixed-point theory as a conformal field
theory having an enhanced SU(2) symmetry and central charge 3/2. While the
fixed point is Lorentz invariant, the effective 'speed of light' nevertheless
vanishes at low energies due to marginally irrelevant operators leading to a
diverging critical specific heat coefficient.Comment: 4 pages, 3 figures, minor changes, published versio
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Numerical investigation of kerosene single droplet ignition at high-altitude relight conditions
In this study, the fundamental problem of the ignition of a
kerosene single droplet in a quiescent medium at engine high-altitude
relight conditions is investigated using numerical simulations. The main
objective is to improve the understanding of ignition phenomena with a
focus on the effect of droplet evaporation in determining the growth of
the ignition kernel and flame establishment. Results show that when the
droplet is fully immersed in a high temperature region, ignition occurs
when the scalar dissipation rate associated with evaporation decreases
enough to allow the initiation of a flame. The ignition time depends on
the droplet diameter and the far field temperature, i.e. the position of
the droplet with respect to the spark location. As the fuel is consumed,
the flame is found to move closer to the droplet surface until the flame
cannot sustain itself any more due to increasing scalar dissipation
rates. Furthermore, results show that at very low temperatures typical of
high-altitude relight conditions no flammable mixture is available around
the droplet. Therefore, the success of an ignition event mainly depends
on the energy released by the spark and the rate at which this energy is
diffused toward the droplet surface to enhance the evaporation rate and
create a flammable mixture. The findings are analysed from the
perspective of gas turbine applications
A New Versatile System for Freeze-Substitution, Freeze-Drying and Low Temperature Embedding of Biological Specimens
A universal system for freeze-substitution (FS), freeze-drying (FD) and low temperature embedding (LTE) has been developed, suited to perform standardized procedures of cryoprocessing biological and medical specimens as well as systematic studies of dehydration and embedding at various low and high temperatures. In a 35 I Dewar vessel with 110 mm neck diameter an aluminum tube is mounted to the bottom of the liquid nitrogen (LN2x) reservoir and extends to the lower part of the cylindrical neck. At its top an aluminum plate serves as a contact surface for either the FS chamber or the FD chamber. FS and subsequent LTE are carried out in an environment of dry cold nitrogen gas provided by evaporating nitrogen from the dewar. Different capsules and moulds may be used for cryodehydration and LTE. FD of bulk specimens or cryosections takes place in an absolutely clean vacuum provided by a cryosorption pump integrated in the FD apparatus. Most of the Hp molecules from the frozen specimen are trapped by large cold surfaces inside the drying chamber. Due to the low LN2 consumption during FS or FD (3-4 l LN2/day) both procedures may be carried out for 8-10 days without refilling the dewar. A few representative results show that well frozen biological material is stabilized by prolonged FS or FD at temperatures of about -80°C without use of chemical fixatives like OsO4 in the substitution medium during FS or by OsO4 vapor fixation after FD
Voltage-Controlled High-Bandwidth Terahertz Oscillators Based On Antiferromagnets
Producing compact voltage-controlled frequency generators and sensors
operating in the terahertz (THz) regime represents a major technological
challenge. Here, we show that noncollinear antiferromagnets (NCAFM) with kagome
structure host gapless self-oscillations whose frequencies are tunable from 0
Hz to the THz regime via electrically induced spin-orbit torques (SOTs). The
auto-oscillations' initiation, bandwidth, and amplitude are investigated by
deriving an effective theory, which captures the reactive and dissipative SOTs.
We find that the dynamics strongly depends on the ground state's chirality,
with one chirality having gapped excitations, whereas the opposite chirality
provides gapless self-oscillations. Our results reveal that NCAFMs offer unique
THz functional components, which could play a significant role in filling the
THz technology gap.Comment: 6 pages, 2 figure
Perspective on unconventional computing using magnetic skyrmions
Learning and pattern recognition inevitably requires memory of previous
events, a feature that conventional CMOS hardware needs to artificially
simulate. Dynamical systems naturally provide the memory, complexity, and
nonlinearity needed for a plethora of different unconventional computing
approaches. In this perspective article, we focus on the unconventional
computing concept of reservoir computing and provide an overview of key
physical reservoir works reported. We focus on the promising platform of
magnetic structures and, in particular, skyrmions, which potentially allow for
low-power applications. Moreover, we discuss skyrmion-based implementations of
Brownian computing, which has recently been combined with reservoir computing.
This computing paradigm leverages the thermal fluctuations present in many
skyrmion systems. Finally, we provide an outlook on the most important
challenges in this field.Comment: 19 pages and 3 figure
Antibiotic-producing symbionts dynamically transition between plant pathogenicity and insect-defensive mutualism
Pathogenic and mutualistic bacteria associated with eukaryotic hosts often lack distinctive genomic features, suggesting regular transitions between these lifestyles. Here we present evidence supporting a dynamic transition from plant pathogenicity to insect-defensive mutualism in symbiotic Burkholderia gladioli bacteria. In a group of herbivorous beetles, these symbionts protect the vulnerable egg stage against detrimental microbes. The production of a blend of antibiotics by B. gladioli, including toxoflavin, caryoynencin and two new antimicrobial compounds, the macrolide lagriene and the isothiocyanate sinapigladioside, likely mediate this defensive role. In addition to vertical transmission, these insect symbionts can be exchanged via the host plant and retain the ability to initiate systemic plant infection at the expense of the plant’s fitness. Our findings provide a paradigm for the transition between pathogenic and mutualistic lifestyles and shed light on the evolution and chemical ecology of this defensive mutualism
CHARGE syndrome and related disorders:A mechanistic link
CHARGE syndrome is an autosomal dominant malformation disorder caused by pathogenic variants in the chromatin remodeler CHD7. Affected are craniofacial structures, cranial nerves and multiple organ systems. Depending on the combination of malformations present, its distinction from other congenital disorders can be challenging. To gain a better insight into the regulatory disturbances in CHARGE syndrome, we performed RNA-Seq analysis on blood samples of 19 children with CHARGE syndrome and a confirmed disease-causing CHD7 variant in comparison to healthy control children. Our analysis revealed a distinct CHARGE syndrome pattern with downregulation of genes that are linked to disorders described to mimic the CHARGE phenotype, i.e. KMT2D and KDM6A (Kabuki syndrome), EP300 and CREBBP (Rubinstein-Taybi syndrome) and ARID1A and ARID1B (Coffin-Siris syndrome). Furthermore, by performing protein-protein interaction studies using co-immunoprecipitation, direct yeast-two hybrid and in situ proximity ligation assays, we could demonstrate an interplay between CHD7, KMT2D, KDM6A and EP300. In summary, our data demonstrate a mechanistic and regulatory link between the developmental disorders CHARGE-, Kabuki- and Rubinstein Taybi-syndrome providing an explanation for the overlapping phenotypes
A-Priori Validation of Scalar Dissipation Rate Models for Turbulent Non-Premixed Flames
Funder: Engineering and Physical Sciences Research Council; doi: http://dx.doi.org/10.13039/501100000266Funder: University of CambridgeAbstract: The modelling of scalar dissipation rate in conditional methods for large-eddy simulations is investigated based on a priori direct numerical simulation analysis using a dataset representing an igniting non-premixed planar jet flame. The main objective is to provide a comprehensive assessment of models typically used for large-eddy simulations of non-premixed turbulent flames with the Conditional Moment Closure combustion model. The linear relaxation model gives a good estimate of the Favre-filtered scalar dissipation rate throughout the ignition with a value of the related constant close to the one deduced from theoretical arguments. Such value of the constant is one order of magnitude higher than typical values used in Reynolds-averaged approaches. The amplitude mapping closure model provides a satisfactory estimate of the conditionally filtered scalar dissipation rate even in flows characterised by shear driven turbulence and strong density variation
Physical and functional interaction between the dopamine transporter and the synaptic vesicle protein synaptogyrin-3.
Uptake through the dopamine transporter (DAT) represents the primary mechanism used to terminate dopaminergic transmission in brain. Although it is well known that dopamine (DA) taken up by the transporter is used to replenish synaptic vesicle stores for subsequent release, the molecular details of this mechanism are not completely understood. Here, we identified the synaptic vesicle protein synaptogyrin-3 as a DAT interacting protein using the split ubiquitin system. This interaction was confirmed through coimmunoprecipitation experiments using heterologous cell lines and mouse brain. DAT and synaptogyrin-3 colocalized at presynaptic terminals from mouse striatum. Using fluorescence resonance energy transfer microscopy, we show that both proteins interact in live neurons. Pull-down assays with GST (glutathione S-transferase) proteins revealed that the cytoplasmic N termini of both DAT and synaptogyrin-3 are sufficient for this interaction. Furthermore, the N terminus of DAT is capable of binding purified synaptic vesicles from brain tissue. Functional assays revealed that synaptogyrin-3 expression correlated with DAT activity in PC12 and MN9D cells, but not in the non-neuronal HEK-293 cells. These changes were not attributed to changes in transporter cell surface levels or to direct effect of the protein-protein interaction. Instead, the synaptogyrin-3 effect on DAT activity was abolished in the presence of the vesicular monoamine transporter-2 (VMAT2) inhibitor reserpine, suggesting a dependence on the vesicular DA storage system. Finally, we provide evidence for a biochemical complex involving DAT, synaptogyrin-3, and VMAT2. Collectively, our data identify a novel interaction between DAT and synaptogyrin-3 and suggest a physical and functional link between DAT and the vesicular DA system
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