Jensen (Can. J. Phys.
98
, 506 (2020). doi:
10.1139/cjp-2019-0395
) presents theoretical justification for the claim that linear triatomic molecules are necessarily observed to be bent. The basis of ...the assertion is that the expectation value of the supplement of the bending angle,
used in Jensen’s paper, is calculated to be positive. In this comment, we examine the interpretation of the expectation values of
in stationary states, and indicate that Jensen’s claim contradicts a basic principle of quantum mechanics that the energy and geometrical variables cannot have definite values at the same time.
Explosive phenomena such as supernova remnant shocks and solar flares have demonstrated evidence for the production of relativistic particles. Interest has therefore been renewed in collisionless ...shock waves and magnetic reconnection as a means to achieve such energies. Although ions can be energized during such phenomena, the relativistic energy of the electrons remains a puzzle for theory. We present supercomputer simulations showing that efficient electron energization can occur during turbulent magnetic reconnection arising from a strong collisionless shock. Upstream electrons undergo first-order Fermi acceleration by colliding with reconnection jets and magnetic islands, giving rise to a nonthermal relativistic population downstream. These results shed new light on magnetic reconnection as an agent of energy dissipation and particle acceleration in strong shock waves.
We use the Magnetospheric Multiscale mission (MMS) to study electron acceleration at Earth's quasi‐perpendicular bow shock to address the long‐standing electron injection problem. The observations ...are compared to the predictions of the stochastic shock drift acceleration (SSDA) theory. Recent studies based on SSDA predict electron distribution being a power law with a cutoff energy that scales with upstream parameters. This scaling law has been successfully tested for a single Earth's bow shock crossing by MMS. Here we extend this study and test the prediction of the scaling law for seven MMS Earth's bow shock crossings with different upstream parameters. A goodness‐of‐fit test shows good agreement between observations and SSDA theoretical predictions, thus supporting SSDA as one of the most promising candidates for solving the electron injection problem.
Plain Language Summary
Collisionless shock waves are an important source of accelerating electrons up to cosmic ray energies throughout our universe. Common electron acceleration mechanisms, explaining the highly relativistic energies observed in cosmic rays, require a population of pre‐accelerated electrons up to mildly relativistic energies of around 0.1–1 MeV. This is known as the electron injection problem and a lot of research is currently spent on studying this pre‐acceleration phase of electron acceleration. We use spacecraft data from the Magnetospheric Multiscale mission to study an electron acceleration mechanism able to accelerate electrons from typical solar wind energies of 20 eV up to around 100 keV. One of the most promising theories for explaining electron acceleration is the so‐called stochastic drift acceleration theory, which involves electron interaction with plasma waves forming within a shock. We provide additional observational evidence supporting this theory.
Key Points
Using Magnetospheric Multiscale data to observe energetic electron events at Earth's collisionless bow shock
Electron acceleration at all crossings is well described by the Stochastic Shock Drift Acceleration Theory
Pitch angle diffusion rate depends on Alfvénic Mach number and shock angle (θBn)
Cohesin is important for 3D genome organization. Nevertheless, even the complete removal of cohesin has surprisingly little impact on steady-state gene transcription and enhancer activity. Here we ...show that cohesin is required for the core transcriptional response of primary macrophages to microbial signals, and for inducible enhancer activity that underpins inflammatory gene expression. Consistent with a role for inflammatory signals in promoting myeloid differentiation of hematopoietic stem and progenitor cells (HPSCs), cohesin mutations in HSPCs led to reduced inflammatory gene expression and increased resistance to differentiation-inducing inflammatory stimuli. These findings uncover an unexpected dependence of inducible gene expression on cohesin, link cohesin with myeloid differentiation, and may help explain the prevalence of cohesin mutations in human acute myeloid leukemia.
The structure of the magnetic reconnection region and the acceleration mechanism of particles as they traverse from upstream into the reconnection exhaust are explored using 2.5D hybrid simulations. ...The reconnection boundary was analyzed using the Rankine‐Hugoniot conditions and the six specific conditions for slow‐mode shocks. We observe that the reconnection boundary can be interpreted as a slow‐mode shock from as close as ∼9 λi ${\lambda }_{i}$ (λi ${\lambda }_{i}$ = ion inertial length) from the X‐point. The detection of slow‐mode shocks increases with the increasing distance from the X‐point and with the increasing ion plasma beta. Additionally, it is observed that if the slow‐mode shocks are analyzed by taking artificial satellite cuts at various angles, the detection percentage of slow‐mode shocks can decrease to ∼10% for very oblique crossings. The detection percentage of slow‐mode shocks is the percentage of points out of the total points studied, where the slow‐mode shocks were observed. At the point of incidence into the slow‐mode shocks, cold particles get accelerated and they gain energy. However, as we move further from the X‐point, a nonclassical picture of slow‐mode shocks emerges, where accelerated particles are present in the downstream of the slow‐mode shocks, but they are not accelerated in the immediate vicinity of the shock. This crescent‐shaped beam population is first accelerated at the slow‐mode shock much closer to the X‐point, and then it travels to the slow‐mode shock downstream region further away from the X‐point, gaining energy on the way by reflecting between the two slow‐mode shocks.
Key Points
Slow‐mode shocks can be detected from ∼9 λi ${\lambda }_{i}$, and their detection increases with increasing plasma beta and the distance from the X‐point
The slow‐mode shock detection percentage can drop to as low as ∼10% if the crossing angle of the satellite is very oblique
Close to the X‐point (≲ $\lesssim $45 λi ${\lambda }_{i}$), the classical picture of slow‐mode shocks is valid, as they directly accelerate the downstream population
Short-chain fatty acids (SCFAs) are fermentation end products produced by the intestinal microbiota and have anti-inflammatory and histone deacetylase-inhibiting properties. Recently, a dual ...relationship between the intestine and kidneys has been unraveled. Therefore, we evaluated the role of SCFA in an AKI model in which the inflammatory process has a detrimental role. We observed that therapy with the three main SCFAs (acetate, propionate, and butyrate) improved renal dysfunction caused by injury. This protection was associated with low levels of local and systemic inflammation, oxidative cellular stress, cell infiltration/activation, and apoptosis. However, it was also associated with an increase in autophagy. Moreover, SCFAs inhibited histone deacetylase activity and modulated the expression levels of enzymes involved in chromatin modification. In vitro analyses showed that SCFAs modulated the inflammatory process, decreasing the maturation of dendritic cells and inhibiting the capacity of these cells to induce CD4(+) and CD8(+) T cell proliferation. Furthermore, SCFAs ameliorated the effects of hypoxia in kidney epithelial cells by improving mitochondrial biogenesis. Notably, mice treated with acetate-producing bacteria also had better outcomes after AKI. Thus, we demonstrate that SCFAs improve organ function and viability after an injury through modulation of the inflammatory process, most likely via epigenetic modification.
Aims. Recently a tentative identification of CH2D+ in interstellar space has been reported. To facilitate astronomical identifications, laboratory measurements of precise rest frequencies for the ...rotational lines of CH2D+ should be carried out. Methods. A submillimeter-wave spectrometer is used for detection of CH2D+. The CH2D+ ion is generated in an extended negative glow discharge operated at liquid nitrogen temperature. The optimum gas mixture is found to be CH4 (~3 mTorr), CD4 (~1 mTorr), and H2 (~2 mTorr) in helium buffer. Results. Four rotational lines have been detected in the frequency range of 280–890 GHz. The measured frequencies agree very well within a MHz with the predictions given by Rösslein et al. from the infrared spectra. Conclusions. Two rotational lines of this ion have been tentatively identified toward Ori IRc2. The rest frequencies obtained here should facilitate identifications and analysis of astronomical spectra.
Purpose
We examined whether eccrine sweat glands ion reabsorption rate declined with age in 35 adults aged 50–84 years. Aerobic fitness (VO
2max
) and salivary aldosterone were measured to see if ...they modulated ion reabsorption rates.
Methods
During a passive heating protocol (lower leg 42 °C water submersion) the maximum ion reabsorption rates from the chest, forearm and thigh were measured, alongside other thermophysiological responses. The maximum ion reabsorption rate was defined as the inflection point in the slope of the relation between galvanic skin conductance and sweat rate.
Results
The maximum ion reabsorption rate at the forearm, chest and thigh (0.29 ± 0.16, 0.33 ± 0.15, 0.18 ± 0.16 mg/cm
2
/min, respectively) were weakly correlated with age (
r
≤ − 0.232,
P
≥ 0.05) and salivary aldosterone concentrations (
r
≤ − 0.180,
P
≥ 0.179). A moderate positive correlation was observed between maximum ion reabsorption rate at the thigh and VO
2max
(
r
= 0.384,
P
= 0.015). Salivary aldosterone concentration moderately declined with age (
r
= − 0.342,
P
= 0.021). Whole body sweat rate and pilocarpine-induced sudomotor responses to iontophoresis increased with VO
2max
(
r
≥ 0.323,
P
≤ 0.027) but only moderate (
r
= − 0.326,
P
= 0.032) or no relations (
r
≤ − 0.113,
P
≥ 0.256) were observed with age.
Conclusion
The eccrine sweat glands’ maximum ion reabsorption rate is not affected by age, spanning 50–84 years. Aldosterone concentration in an aged cohort does not appear to modulate the ion reabsorption rate. We provide further support for maintaining cardiorespiratory fitness to attenuate any decline in sudomotor function.
The first-order Fermi acceleration of electrons requires an injection of electrons into a mildly relativistic energy range. However, the mechanism of injection has remained a puzzle both in theory ...and observation. We present direct evidence for a novel stochastic shock drift acceleration theory for the injection obtained with Magnetospheric Multiscale observations at the Earth's bow shock. The theoretical model can explain electron acceleration to mildly relativistic energies at high-speed astrophysical shocks, which may provide a solution to the long-standing issue of electron injection.
Abstract
Charge acceleration during an intense light field application to solids attracts much attention as elementary processes in high-harmonic generation and photoelectron emission. For ...manipulating such attosecond dynamics of charge, carrier-envelope-phase (CEP: relative phase between carrier oscillation of light field and its envelope function) control has been employed in insulators, nanometal and graphene. In superconducting materials, collective control of charge motion is expected because of its strongly coherent nature of quasi-particles. Here we report that, in a layered organic superconductor, a non-linear petahertz current driven by a single-cycle 6 femtosecond near infrared field shows up as second harmonic generation (SHG), which is in contrast to the common belief that even harmonics are forbidden in the centrosymmetric system. The SHG represents a CEP sensitive nature and an enhancement near the superconducting temperature. The result and its quantum many-body analysis indicate that a polarized current is induced by non-linear acceleration of charge, which is amplified by superconducting fluctuations. This will lead to petahertz functions of superconductors and of strongly correlated systems.
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