We introduce a theory of modules over a representation of a small category taking values in entwining structures over a semiperfect coalgebra. This takes forward the aim of developing categories of ...entwined modules to the same extent as that of module categories as well as the philosophy of Mitchell of working with rings with several objects. The representations are motivated by work of Estrada and Virili, who developed a theory of modules over a representation taking values in small preadditive categories, which were then studied in the same spirit as sheaves of modules over a scheme. We also describe, by means of Frobenius and separable functors, how our theory relates to that of modules over the underlying representation taking values in small
K
-linear categories.
For a
k
-algebra
A
, the category
of
A
-modules taking values in a
k
-linear abelian category
was introduced by Popescu. The algebraic properties of
, including Grothendieck’s theory of flat descent, ...were developed by Artin and Zhang. In this note, we show that Beauville–Laszlo descent also holds in the category
.
A
bstract
Cosmological relaxation of the electroweak scale is an attractive scenario addressing the gauge hierarchy problem. Its main actor, the relaxion, is a light spin-zero field which dynamically ...relaxes the Higgs mass with respect to its natural large value. We show that the relaxion is generically stabilized at a special position in the field space, which leads to suppression of its mass and potentially unnatural values for the model’s effective low-energy couplings. In particular, we find that the relaxion mixing with the Higgs can be several orders of magnitude above its naive naturalness bound. Low energy observers may thus find the relaxion theory being fine-tuned although the relaxion scenario itself is constructed in a technically natural way. More generally, we identify the lower and upper bounds on the mixing angle. We examine the experimental implications of the above observations at the luminosity and precision frontiers. A particular attention is given to the impressive ability of future nuclear clocks to search for rapidly oscillating scalar ultra-light dark matter, where the future projected sensitivity is presented.
Probing gene function in the mammalian brain can be greatly assisted with methods to manipulate the genome of neurons in vivo. The clustered, regularly interspaced, short palindromic repeats ...(CRISPR)-associated endonuclease (Cas)9 from Streptococcus pyogenes (SpCas9) can be used to edit single or multiple genes in replicating eukaryotic cells, resulting in frame-shifting insertion/deletion (indel) mutations and subsequent protein depletion. Here, we delivered SpCas9 and guide RNAs using adeno-associated viral (AAV) vectors to target single (Mecp2) as well as multiple genes (Dnmt1, Dnmt3a and Dnmt3b) in the adult mouse brain in vivo. We characterized the effects of genome modifications in postmitotic neurons using biochemical, genetic, electrophysiological and behavioral readouts. Our results demonstrate that AAV-mediated SpCas9 genome editing can enable reverse genetic studies of gene function in the brain.
In nature, nitrogen fixation is one of the most important life processes and occurs primarily in microbial organisms containing enzymes called nitrogenases. These complex proteins contain two ...distinct subunits with different active sites, with the primary N2 binding site being a FeMoS core cluster that can be reduced by other nearby iron–sulfur clusters. Although nitrogen reduction to ammonia in biology does not require the absorption of light, there is considerable interest in developing catalyst materials that could drive the formation of ammonia from nitrogen photochemically. Here, we report that chalcogels containing FeMoS inorganic clusters are capable of photochemically reducing N2 to NH3 under white light irradiation, in aqueous media, under ambient pressure and room temperature. The chalcogels are composed of Mo2Fe6S8(SPh)33+ and Sn2S64– clusters in solution and have strong optical absorption, high surface area, and good aqueous stability. Our results demonstrate that light-driven nitrogen conversion to ammonia by MoFe sulfides is a viable process with implications in solar energy utilization and our understanding of primordial processes on earth.
GaN-on-Si power switching transistors that use carbon-doped epitaxy are highly vulnerable to dynamic R ON dispersion, leading to reduced switching efficiency. In this paper, we identify the causes of ...this dispersion using substrate bias ramps to isolate the leakage paths and trapping locations in the epitaxy and simulation to identify their impact on the device characteristics. It is shown that leakage can occur both vertically and laterally, and we suggest that this is associated not only with bulk transport, but also with extended defects as well as hole gases at heterojunctions. For exactly the same epitaxial design, it is shown using a "leaky dielectric" model that depending on the leakage paths, dynamic R ON dispersion can vary between insignificant and infinite. An optimum leakage configuration is identified to minimize dispersion requiring a resistivity which increases with depth in the buffer stack. It is demonstrated that leakage through the undoped GaN channel is required over the entire gate to drain gap, and not just under the contacts, in order to fully suppress dispersion.
A
bstract
We discuss models of ultralight scalar Dark Matter (DM) with linear and quadratic couplings to the Standard Model (SM). In addition to studying the phenomenology of linear and quadratic ...interactions separately, we examine their interplay. We review the different experiments that can probe such interactions and present the current and expected future bounds on the parameter space. In particular, we discuss the scalar field solution presented in A. Hees, O. Minazzoli, E. Savalle, Y. V. Stadnik and P. Wolf, Phys.Rev.D 98 (2018) 6, 064051, and extend it to theories that capture both the linear and the quadratic couplings of the Dark Matter (DM) field to the Standard Model (SM). Furthermore, we discuss the theoretical aspects and the corresponding challenges for natural models in which the quadratic interactions are of phenomenological importance.
The cosmological relaxion can address the hierarchy problem, while its coherent oscillations can constitute dark matter in the present universe. We consider the possibility that the relaxion forms ...gravitationally bound objects that we denote as relaxion stars. The density of these stars would be higher than that of the local dark matter density, resulting in enhanced signals in table-top detectors, among others. Furthermore, we raise the possibility that these objects may be trapped by an external gravitational potential, such as that of the Earth or the Sun. This leads to formation of relaxion halos of even greater density. We discuss several interesting implications of relaxion halos, as well as detection strategies to probe them. Here, we show that current and near-future atomic physics experiments can probe physical models of relaxion dark matter in scenarios of bound relaxion halos around the Earth or Sun.The origin of Dark Matter (DM) in the Universe remains one of the main unresolved questions in Cosmology. The authors propose to probe a scenario where DM forms a compact object known as boson star, or a small DM halo bound to the Earth or sun, with a density higher than the local DM density making them detectable via atomic physics table top experiments.
A nitrogenase-inspired biomimetic chalcogel system comprising double-cubane Mo₂Fe₆S₈(SPh)₃ and single-cubane (Fe₄S₄) biomimetic clusters demonstrates photocatalytic N₂ fixation and conversion to NH₃ ...in ambient temperature and pressure conditions. Replacing the Fe₄S₄ clusters in this system with other inert ions such as Sb3+, Sn4+, Zn2+ also gave chalcogels that were photocatalytically active. Finally, molybdenum-free chalcogels containing only Fe₄S₄ clusters are also capable of accomplishing the N₂ fixation reaction with even higher efficiency than their Mo₂Fe₆S₈(SPh)₃-containing counterparts. Our results suggest that redox-active iron-sulfide–containing materials can activate the N₂ molecule upon visible light excitation, which can be reduced all of the way to NH₃ using protons and sacrificial electrons in aqueous solution. Evidently, whereas the Mo₂Fe₆S₈(SPh)₃ is capable of N₂ fixation, Mo itself is not necessary to carry out this process. The initial binding of N₂ with chalcogels under illumination was observed with in situ diffuse-reflectance Fourier transform infrared spectroscopy (DRIFTS). 15N₂ isotope experiments confirm that the generated NH₃ derives from N₂. Density functional theory (DFT) electronic structure calculations suggest that the N₂ binding is thermodynamically favorable only with the highly reduced active clusters. The results reported herein contribute to ongoing efforts of mimicking nitrogenase in fixing nitrogen and point to a promising path in developing catalysts for the reduction of N₂ under ambient conditions.
Contrast enhancement is explored in optical coherence tomography images using core NaYF
4
:Ho
3+
/Yb
3+
and core@shell NaYF
4
:Ho
3+
/Yb
3+
@NaGdF
4
nanoparticles. Under 980 nm excitation, core@shell ...nanoparticles exhibited 2.8 and 3.3 times enhancement at 541 nm and 646 nm emission wavelengths of Ho
3+
ions compared to core nanoparticles. Photo-thermal conversion efficiencies were 32% and 20% for core and core@shell nanoparticles. In swept-source optical coherence tomography (SSOCT), core@shell nanoparticles have shown superior contrast, while in photo-thermal optical coherence tomography (PTOCT) core nanoparticles have excelled due to their higher photo-thermal conversion efficiency. The enhancement in contrast to noise ratio obtained is 58 dB. Comparative assessments of scattering coefficients and contrast-to-noise ratios were conducted, providing insights into nanoparticle performance for contrast enhancement in optical coherence tomography.
Graphical abstract
PDF
