Human mitochondrial transcription factor A (TFAM) is a high-mobility group (HMG) protein at the nexus of mitochondrial DNA (mtDNA) replication, transcription, and inheritance. Little is known about ...the mechanisms underlying its posttranslational regulation. Here, we demonstrate that TFAM is phosphorylated within its HMG box 1 (HMG1) by cAMP-dependent protein kinase in mitochondria. HMG1 phosphorylation impairs the ability of TFAM to bind DNA and to activate transcription. We show that only DNA-free TFAM is degraded by the Lon protease, which is inhibited by the anticancer drug bortezomib. In cells with normal mtDNA levels, HMG1-phosphorylated TFAM is degraded by Lon. However, in cells with severe mtDNA deficits, nonphosphorylated TFAM is also degraded, as it is DNA free. Depleting Lon in these cells increases levels of TFAM and upregulates mtDNA content, albeit transiently. Phosphorylation and proteolysis thus provide mechanisms for rapid fine-tuning of TFAM function and abundance in mitochondria, which are crucial for maintaining and expressing mtDNA.
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► cAMP-dependent protein kinase (PKA) serine phosphorylates TFAM within HMG1 ► HMG1 phosphorylation of TFAM impairs DNA binding and transcription activation ► Lon protease selectively degrades DNA-free TFAM and is inhibited by bortezomib ► Lon knockdown stabilizes TFAM in mtDNA-deficient cells and upregulates mtDNA
We describe monocrystalline graphitic films, which are a few atoms thick but are nonetheless stable under ambient conditions, metallic, and of remarkably high quality. The films are found to be a ...two-dimensional semimetal with a tiny overlap between valence and conductance bands, and they exhibit a strong ambipolar electric field effect such that electrons and holes in concentrations up to 1013per square centimeter and with room-temperature mobilities of ~10,000 square centimeters per volt-second can be induced by applying gate voltage.
Although graphite is known as one of the most chemically inert materials, we have found that graphene, a single atomic plane of graphite, can react with atomic hydrogen, which transforms this highly ...conductive zero-overlap semimetal into an insulator. Transmission electron microscopy reveals that the obtained graphene derivative (graphane) is crystalline and retains the hexagonal lattice, but its period becomes markedly shorter than that of graphene. The reaction with hydrogen is reversible, so that the original metallic state, the lattice spacing, and even the quantum Hall effect can be restored by annealing. Our work illustrates the concept of graphene as a robust atomic-scale scaffold on the basis of which new two-dimensional crystals with designed electronic and other properties can be created by attaching other atoms and molecules.
Quantum electrodynamics (resulting from the merger of quantum mechanics and relativity theory) has provided a clear understanding of phenomena ranging from particle physics to cosmology and from ...astrophysics to quantum chemistry. The ideas underlying quantum electrodynamics also influence the theory of condensed matter, but quantum relativistic effects are usually minute in the known experimental systems that can be described accurately by the non-relativistic Schrödinger equation. Here we report an experimental study of a condensed-matter system (graphene, a single atomic layer of carbon) in which electron transport is essentially governed by Dirac's (relativistic) equation. The charge carriers in graphene mimic relativistic particles with zero rest mass and have an effective 'speed of light' c* 106 m s-1. Our study reveals a variety of unusual phenomena that are characteristic of two-dimensional Dirac fermions. In particular we have observed the following: first, graphene's conductivity never falls below a minimum value corresponding to the quantum unit of conductance, even when concentrations of charge carriers tend to zero; second, the integer quantum Hall effect in graphene is anomalous in that it occurs at half-integer filling factors; and third, the cyclotron mass mc of massless carriers in graphene is described by E = mcc*2. This two-dimensional system is not only interesting in itself but also allows access to the subtle and rich physics of quantum electrodynamics in a bench-top experiment.
Recent developments in the technology of van der Waals heterostructures made from two-dimensional atomic crystals have already led to the observation of new physical phenomena, such as the ...metal-insulator transition and Coulomb drag, and to the realization of functional devices, such as tunnel diodes, tunnel transistors and photovoltaic sensors. An unprecedented degree of control of the electronic properties is available not only by means of the selection of materials in the stack, but also through the additional fine-tuning achievable by adjusting the built-in strain and relative orientation of the component layers. Here we demonstrate how careful alignment of the crystallographic orientation of two graphene electrodes separated by a layer of hexagonal boron nitride in a transistor device can achieve resonant tunnelling with conservation of electron energy, momentum and, potentially, chirality. We show how the resonance peak and negative differential conductance in the device characteristics induce a tunable radiofrequency oscillatory current that has potential for future high-frequency technology.
Thermodiffusion of binary mixtures in an inhomogeneous temperature field is due to scattering phenomena and the effects of interparticle interactions. Accordingly, when describing the Soret ...coefficient, it is customary to distinguish between the kinetic and the chemical contributions. Predicting thermodiffusion even in simple binary mixtures is challenging because of numerous factors that influence these contributions. Here, we present a comprehensive theoretical study of both contributions and make predictions of the Soret coefficient for 141 equimolar binary mixtures composed of 24 nonassociating and non- or weakly polar simple liquids. The chemical contribution is an equilibrium property related to the gradient of a partial pressure of one of the mixture components. It is successfully described within the framework of the perturbed-chain statistical associating fluid theory, characterizing the pure liquids by only three physically significant parameters: the segment number, the hard-core segment diameter, and the segment–segment interaction parameter. The nonequilibrium kinetic contribution is approximated by the relation associated with hydrodynamic fluctuations. The sum of the chemical and kinetic contributions determines the Soret coefficient of the mixture. Both contributions are found for the case of dilute mixtures. The equimolar value of the Soret coefficient is calculated as the arithmetic mean of its limiting values. The predicted values of the Soret coefficient are compared with the experimental data available for 113 mixtures. Overall, the theoretical and experimental results are in good agreement with each other. For 70 mixtures, the difference of data does not exceed 0.002 K–1. The best agreement between the data occurs for the alkanes. The maximum deviations of the results are observed for mixtures with 1-methylnaphthalene, bromonaphthalene, and cyclohexane. We relate these deviations to the plate-like shape of their molecules, which is not taken into account when deriving the kinetic contribution.
Coupled twiss parameters estimation from turn-by-turn data Morozov, I.; Maltseva, Yu
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
September 2024, 2024-09-00, Volume:
1066
Journal Article
Peer reviewed
Open access
Linear optics parameters are often estimated using turn-by-turn (TbT) data. In-plane beta functions, which are the most common measurement objectives, can be estimated from the amplitudes or phases ...of TbT data, providing an overall characterization of the linear lattice. In addition to estimating uncoupled Twiss parameters, TbT data can also be utilized for characterizing coupled linear motion. We investigate several methods for constructing a full normalization matrix at each beam position monitor (BPM). BPMs provide information on beam centroid transverse coordinates, but direct observation of transverse momenta is not available. To estimate momenta, one can use a pair of BPMs or fit data obtained from several BPMs. By using both coordinates and momenta, it is possible to fit the one-turn matrix (or its power) at each BPM, allowing for the computation of coupled Twiss parameters. Another approach involves the minimization of side peak amplitudes in the spectrum of normalized complex coordinates. Similarly, the normalization matrix can be estimated by fitting linear coupled invariants. In this study, we derive and utilize a special form of the normalization matrix, which remains non-singular in the zero coupling limit. Coupled Twiss parameters can be obtained from the normalization matrix. The paper presents the results of applying and comparing these methods to both modeled and measured VEPP-4M TbT data, demonstrating effective estimation of coupled Twiss parameters.
The primate cerebrum is characterized by a large expansion of cortical surface area, the formation of convolutions, and extraordinarily voluminous subcortical white matter. It was recently proposed ...that this expansion is primarily driven by increased production of superficial neurons in the dramatically enlarged outer subventricular zone (oSVZ). Here, we examined the development of the parietal cerebrum in macaque monkey and found that, indeed, the oSVZ initially adds neurons to the superficial layers II and III, increasing their thickness. However, as the oSVZ grows in size, its output changes to production of astrocytes and oligodendrocytes, which in primates outnumber cerebral neurons by a factor of three. After the completion of neurogenesis around embryonic day (E) 90, when the cerebrum is still lissencephalic, the oSVZ enlarges and contains Pax6⁺/Hopx⁺ outer (basal) radial glial cells producing astrocytes and oligodendrocytes until after E125. Our data indicate that oSVZ gliogenesis, rather than neurogenesis, correlates with rapid enlargement of the cerebrum and development of convolutions, which occur concomitantly with the formation of cortical connections via the underlying white matter, in addition to neuronal growth, elaboration of dendrites, and amplification of neuropil in the cortex, which are primary factors in the formation of cerebral convolutions in primates.
The ultimate aim of any detection method is to achieve such a level of sensitivity that individual quanta of a measured entity can be resolved. In the case of chemical sensors, the quantum is one ...atom or molecule. Such resolution has so far been beyond the reach of any detection technique, including solid-state gas sensors hailed for their exceptional sensitivity. The fundamental reason limiting the resolution of such sensors is fluctuations due to thermal motion of charges and defects, which lead to intrinsic noise exceeding the sought-after signal from individual molecules, usually by many orders of magnitude. Here, we show that micrometre-size sensors made from graphene are capable of detecting individual events when a gas molecule attaches to or detaches from graphene's surface. The adsorbed molecules change the local carrier concentration in graphene one by one electron, which leads to step-like changes in resistance. The achieved sensitivity is due to the fact that graphene is an exceptionally low-noise material electronically, which makes it a promising candidate not only for chemical detectors but also for other applications where local probes sensitive to external charge, magnetic field or mechanical strain are required.
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