A
bstract
Leptoquarks have recently received much attention especially because they may provide an explanation to the
R
D
*
and
R
K
*
anomalies in rare
B
meson decays. In a previous paper we proposed ...a systematic search strategy for all possible leptoquark flavors by focusing on leptoquark pair production. In this paper, we extend this strategy to large (order unity) leptoquark couplings which offer new search opportunities: single leptoquark production and
t
-channel leptoquark exchange with dilepton final states. We discuss the unique features of the different search channels and show that they cover complementary regions of parameter space. We collect and update all currently available bounds for the different flavor final states from LHC searches and from atomic parity violation measurements. As an application of our analysis, we find that current limits do not exclude a leptoquark explanation of the
B
physics anomalies but that the high luminosity run of the LHC will reach the most interesting parameter space.
Brain iron transport Qian, Zhong‐Ming; Ke, Ya
Biological reviews of the Cambridge Philosophical Society,
October 2019, 2019-10-00, 20191001, Volume:
94, Issue:
5
Journal Article
Peer reviewed
ABSTRACT
Brain iron is a crucial participant and regulator of normal physiological activity. However, excess iron is involved in the formation of free radicals, and has been associated with oxidative ...damage to neuronal and other brain cells. Abnormally high brain iron levels have been observed in various neurodegenerative diseases, including neurodegeneration with brain iron accumulation, Alzheimer's disease, Parkinson's disease and Huntington's disease. However, the key question of why iron levels increase in the relevant regions of the brain remains to be answered. A full understanding of the homeostatic mechanisms involved in brain iron transport and metabolism is therefore critical not only for elucidating the pathophysiological mechanisms responsible for excess iron accumulation in the brain but also for developing pharmacological interventions to disrupt the chain of pathological events occurring in these neurodegenerative diseases. Numerous studies have been conducted, but to date no effort to synthesize these studies and ideas into a systematic and coherent summary has been made, especially concerning iron transport across the luminal (apical) membrane of the capillary endothelium and the membranes of different brain cell types. Herein, we review key findings on brain iron transport, highlighting the mechanisms involved in iron transport across the luminal (apical) as well as the abluminal (basal) membrane of the blood–brain barrier, the blood–cerebrospinal fluid barrier, and iron uptake and release in neurons, oligodendrocytes, astrocytes and microglia within the brain. We offer suggestions for addressing the many important gaps in our understanding of this important topic, and provide new insights into the potential causes of abnormally increased iron levels in regions of the brain in neurodegenerative disorders.
Abnormally high brain iron, resulting from the disrupted expression or function of proteins involved in iron metabolism in the brain, is an initial cause of neuronal death in neuroferritinopathy and ...aceruloplasminemia, and also plays a causative role in at least some of the other neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, Huntington's disease, and Friedreich's ataxia. As such, iron is believed to be a novel target for pharmacological intervention in these disorders. Reducing iron toward normal levels or hampering the increases in iron associated with age in the brain is a promising therapeutic strategy for all iron‐related neurodegenerative disorders. Hepcidin is a crucial regulator of iron homeostasis in the brain. Recent studies have suggested that upregulating brain hepcidin levels can significantly reduce brain iron content through the regulation of iron transport protein expression in the blood‐brain barrier and in neurons and astrocytes. In this review, we focus on the discussion of the therapeutic potential of hepcidin in iron‐associated neurodegenerative diseases and also provide a systematic overview of recent research progress on how misregulated brain iron metabolism is involved in the development of multiple neurodegenerative disorders.
Piezoelectric polymers hold great potential for various electromechanical applications, but only show low performance, with |d
| < 30 pC/N. We prepare a highly piezoelectric polymer (d
= -62 pC/N) ...based on a biaxially oriented poly(vinylidene fluoride) (BOPVDF, crystallinity = 0.52). After unidirectional poling, macroscopically aligned samples with pure β crystals are achieved, which show a high spontaneous polarization (P
) of 140 mC/m
. Given the theoretical limit of P
= 188 mC/m
for the neat β crystal, the high P
cannot be explained by the crystalline-amorphous two-phase model (i.e., P
= 270 mC/m
). Instead, we deduce that a significant amount (at least 0.25) of an oriented amorphous fraction (OAF) must be present between these two phases. Experimental data suggest that the mobile OAF resulted in the negative and high d
for the poled BOPVDF. The plausibility of this conclusion is supported by molecular dynamics simulations.
A high‐performance electromagnetic interference shielding composite based on reduced graphene oxide (rGO) and polystyrene (PS) is realized via high‐pressure solid‐phase compression molding. Superior ...shielding effectiveness of 45.1 dB, the highest value among rGO based polymer composite, is achieved with only 3.47 vol% rGO loading owning to multi‐facet segregated architecture with rGO selectively located on the boundaries among PS multi‐facets. This special architecture not only provides many interfaces to absorb the electromagnetic waves, but also dramatically reduces the loading of rGO by confining the rGO at the interfaces. Moreover, the mechanical strength of the segregated composite is dramatically enhanced using high pressure at 350 MPa, overcoming the major disadvantage of the composite made by conventional‐pressure (5 MPa). The composite prepared by the higher pressure shows 94% and 40% increment in compressive strength and compressive modulus, respectively. These results demonstrate a promising method to fabricate an economical, robust, and highly efficient EMI shielding material.
The rGO/PS composite with segregated architecture is realized via high‐pressure solid‐phase compression molding for efficient EMI shielding. The highest EMI SE of 45.1 dB among rGO based polymer composites is achieved with only 3.47 vol% rGO loading. The high‐pressure molded composite shows 94% and 40% enhancement in compressive strength and modulus compared to conventional‐pressure molded composite.
A series of highly luminescent‐active metal–organic frameworks (MOFs) 1–3 with hierarchical pores have been rationally constructed and fully characterized. The predesigned semi‐rigid hexacarboxylate ...ligand hexa4‐(carboxyphenyl)oxamethyl‐3‐oxapentane acid (H6L) has been adapted with various space‐directed N donors (i.e., 2,2’‐bipyridine, 4,4′‐di(1H‐imidazol‐1‐yl)‐1,1′‐biphenyl, and 1,3,5‐tri(1H‐imidazol‐1‐yl)benzene) from a bidentate V‐shape to a tridentate Y‐shape. This family of multifunctional MOF materials represents a variety of potential applications in the following aspects: first, as luminescent sensors that show a fast and sensitive detection for pollutant CrO42− and Cr2O72− ions in aqueous media; second, as adsorbents that can rapidly remove harmful organic dyes; third, as an antenna that can effectively sensitize visible‐light‐emitting Tb3+ ions. These multifunctional MOF materials combine optical‐sensing, adsorption, and sensitization properties, thus are very useful in many potential applications. Furthermore, these materials have proved to be reusable.
All in one: A series of multifunctional cadmium metal–organic frameworks (MOFs) has been rationally constructed that combines sensor properties for the excellent detection of pollutant CrO42− and Cr2O72− ions, sensitizer properties for the effective and selective sensitization of the visible‐emitting Tb3+ ion in aqueous media, and absorbent abilities for the fast removal of the methylene blue (MB) dye. Furthermore, these MOF materials are recyclable (see figure).
Originally, the concepts of aromaticity and antiaromaticity were introduced to explain the stability and reactivity of unsaturated organic compounds. Since then, they have been extended to other ...species with delocalized electrons including various saturated systems, organometallic compounds, and even inorganic clusters and molecules. In this Minireview, we focus on the most recent progress of using these concepts to guide experimental synthesis and rationalize geometrical and electronic structures of a particular family of polyanions composed of Group 14 and 15 elements, namely Zintl clusters.
Bonding in a cluster: The application of concepts of aromaticity and antiaromaticity towards Zintl clusters is discussed in this minireview.
A
bstract
Leptoquarks occur in many new physics scenarios and could be the next big discovery at the LHC. The purpose of this paper is to point out that a model-independent search strategy covering ...all possible leptoquarks is possible and has not yet been fully exploited. To be systematic we organize the possible leptoquark final states according to a leptoquark matrix with entries corresponding to nine experimentally distinguishable leptoquark decays: any of {light-jet,
b
-jet, top} with any of {neutrino,
e
/
μ
,
τ
}. The 9 possibilities can be explored in a largely model-independent fashion with pair-production of leptoquarks at the LHC. We review the status of experimental searches for the 9 components of the leptoquark matrix, pointing out which 3 have not been adequately covered. We plead that experimenters publish bounds on leptoquark cross sections as functions of mass for as wide a range of leptoquark masses as possible. Such bounds are essential for reliable recasts to general leptoquark models. To demonstrate the utility of the leptoquark matrix approach we collect and summarize searches with the same final states as leptoquark pair production and use them to derive bounds on a complete set of Minimal Leptoquark models which span all possible flavor and gauge representations for scalar and vector leptoquarks.
Orchidaceae (with >28,000 orchid species) are one of the two largest plant families, with economically and ecologically important species, and occupy global and diverse niches with primary ...distribution in rainforests. Among orchids, 70% grow on other plants as epiphytes; epiphytes contribute up to ~50% of the plant diversity in rainforests and provide food and shelter for diverse animals and microbes, thereby contributing to the health of these ecosystems. Orchids account for over two‐thirds of vascular epiphytes and provide an excellent model for studying evolution of epiphytism. Extensive phylogenetic studies of Orchidaceae and subgroups have ;been crucial for understanding relationships among many orchid lineages, although some uncertainties remain. For example, in the largest subfamily Epidendroideae with nearly all epiphytic orchids, relationships among some tribes and many subtribes are still controversial, hampering evolutionary analyses of epiphytism. Here we obtained 1,450 low‐copy nuclear genes from 610 orchid species, including 431 with newly generated transcriptomes, and used them for the reconstruction of robust Orchidaceae phylogenetic trees with highly supported placements of tribes and subtribes. We also provide generally well‐supported phylogenetic placements of 131 genera and 437 species that were not sampled by previous plastid and nuclear phylogenomic studies. Molecular clock analyses estimated the Orchidaceae origin at ~132 million years ago (Ma) and divergences of most subtribes from 52 to 29 Ma. Character reconstruction supports at least 14 parallel origins of epiphytism; one such origin was placed at the most recent common ancestor of ~95% of epiphytic orchids and linked to modern rainforests. Ten occurrences of rapid increase in the diversification rate were detected within Epidendroideae near and after the K‐Pg boundary, contributing to ~80% of the Orchidaceae diversity. This study provides a robust and the largest family‐wide Orchidaceae nuclear phylogenetic tree thus far and new insights into the evolution of epiphytism in vascular plants.
Orchidaceae are one of two largest angiosperm families with ~28,000 species and mainly grow as epiphytes on trees in rainforests. Evolutionary analyses of 610 orchids with 431 new transcriptomes provides a robust Orchidaceae phylogeny and suggests that the expansion of rainforests probably promoted the origin and diversification of epiphytic orchids.
A
bstract
We initiate a systematic study of precision calculation of the inflation correlators at the 1-loop level, starting in this paper with bosonic 1-loop bispectrum with chemical-potential ...enhancement. Such 1-loop processes could lead to important cosmological collider observables but are notoriously difficult to compute due to the lack of symmetries. We attack the problem from a direct numerical approach based on the real-time Schwinger-Keldysh formalism and show full numerical results for arbitrary kinematics containing both the oscillatory “signals” and the “backgrounds”. Our results show that, while the non-oscillatory part can be one to two orders of magnitude larger, the oscillatory signal can be separated out by applying appropriate high-pass filters. We have also compared the result with analytic estimates typically adopted in the literature. While the amplitude is comparable, there is a non-negligible deviation in the frequency of the oscillatory part away from the extreme squeezed limit.
PDF
