38 research outputs found
Observation of the nonlinear Hall effect under time reversal symmetric conditions
The electrical Hall effect is the production of a transverse voltage under an
out-of-plane magnetic field. Historically, studies of the Hall effect have led
to major breakthroughs including the discoveries of Berry curvature and the
topological Chern invariants. In magnets, the internal magnetization allows
Hall conductivity in the absence of external magnetic field. This anomalous
Hall effect (AHE) has become an important tool to study quantum magnets. In
nonmagnetic materials without external magnetic fields, the electrical Hall
effect is rarely explored because of the constraint by time-reversal symmetry.
However, strictly speaking, only the Hall effect in the linear response regime,
i.e., the Hall voltage linearly proportional to the external electric field,
identically vanishes due to time-reversal symmetry. The Hall effect in the
nonlinear response regime, on the other hand, may not be subject to such
symmetry constraints. Here, we report the observation of the nonlinear Hall
effect (NLHE) in the electrical transport of the nonmagnetic 2D quantum
material, bilayer WTe2. Specifically, flowing an electrical current in bilayer
WTe2 leads to a nonlinear Hall voltage in the absence of magnetic field. The
NLHE exhibits unusual properties sharply distinct from the AHE in metals: The
NLHE shows a quadratic I-V characteristic; It strongly dominates the nonlinear
longitudinal response, leading to a Hall angle of about 90 degree. We further
show that the NLHE directly measures the "dipole moment" of the Berry
curvature, which arises from layer-polarized Dirac fermions in bilayer WTe2.
Our results demonstrate a new Hall effect and provide a powerful methodology to
detect Berry curvature in a wide range of nonmagnetic quantum materials in an
energy-resolved way
Hidden attractors in fundamental problems and engineering models
Recently a concept of self-excited and hidden attractors was suggested: an
attractor is called a self-excited attractor if its basin of attraction
overlaps with neighborhood of an equilibrium, otherwise it is called a hidden
attractor. For example, hidden attractors are attractors in systems with no
equilibria or with only one stable equilibrium (a special case of
multistability and coexistence of attractors). While coexisting self-excited
attractors can be found using the standard computational procedure, there is no
standard way of predicting the existence or coexistence of hidden attractors in
a system. In this plenary survey lecture the concept of self-excited and hidden
attractors is discussed, and various corresponding examples of self-excited and
hidden attractors are considered
Intergenomic Rearrangements after Polyploidization of Kengyilia thoroldiana (Poaceae: Triticeae) Affected by Environmental Factors
Polyploidization is a major evolutionary process. Approximately 70ā75% species of Triticeae (Poaceae) are polyploids, involving 23 genomes. To investigate intergenomic rearrangements after polyploidization of Triticeae species and to determine the effects of environmental factors on them, nine populations of a typical polyploid Triticeae species, Kengyilia thoroldiana (Keng) J.L.Yang et al. (2nā=ā6xā=ā42, StStPPYY), collected from different environments, were studied using genome in situ hybridization (GISH). We found that intergenomic rearrangements occurred between the relatively large P genome and the small genomes, St (8.15%) and Y (22.22%), in polyploid species via various types of translocations compared to their diploid progenitors. However, no translocation was found between the relatively small St and Y chromosomes. Environmental factors may affect rearrangements among the three genomes. Chromosome translocations were significantly more frequent in populations from cold alpine and grassland environments than in populations from valley and lake-basin habitats (P<0.05). The relationship between types of chromosome translocations and altitude was significant (rā=ā0.809, P<0.01). Intergenomic rearrangements associated with environmental factors and genetic differentiation of a single basic genome should be considered as equally important genetic processes during species' ecotype evolution
NC1-peptide derived from collagen Ī±3 (IV) chain is a blood-tissue barrier regulator: Lesson from the testis
Collagen Ī±3 (IV) chains are one of the major constituent components of the basement membrane in the mammalian testis. Studies have shown that biologically active fragments, such as noncollagenase domain (NC1)-peptide, can be released from the C-terminal region of collagen Ī±3 (IV) chains, possibly through the proteolytic action of metalloproteinase 9 (MMP9). NC1-peptide was shown to promote bloodātestis barrier (BTB) remodeling and fully developed spermatid (e.g., sperm) release from the seminiferous epithelium because this bioactive peptide was capable of perturbing the organization of both actin- and microtubule (MT)-based cytoskeletons at the Sertoli cellācell and also Sertoliāspermatid interface, the ultrastructure known as the basal ectoplasmic specialization (ES) and apical ES, respectively. More importantly, recent studies have shown that this NC1-peptide-induced effects on cytoskeletal organization in the testis are mediated through an activation of mammalian target of rapamycin complex 1/ribosomal protein S6/transforming retrovirus Akt1/2 protein (mTORC1/rpS6/Akt1/2) signaling cascade, involving an activation of cell division control protein 42 homolog (Cdc42) GTPase, but not Ras homolog family member A GTPase (RhoA), and the participation of end-binding protein 1 (EB1), a microtubule plus (+) end tracking protein (+TIP), downstream. Herein, we critically evaluate these findings, providing a critical discussion by which the basement membrane modulates spermatogenesis through one of its locally generated regulatory peptides in the testis
NC1-peptide from collagen Ī±3 (IV) chains in the basement membrane of testes regulates spermatogenesis via p-FAK-Y407
The blood-testis barrier (BTB) in the testis is an important ultrastructure to support spermatogenesis. This blood-tissue barrier undergoes remodeling at late stage VII-early stage IX of the epithelial cycle to support the transport of preleptotene spermatocytes across the BTB to prepare for meiosis I/II at the apical compartment through a mechanism that remains to be delineated.. Studies have shown that NC1-peptide derived collagen Ī±3 (IV) chain in the basement membrane, is a bioactive peptide that induces BTB remodeling. It also promotes the release of fully developed spermatids into the tubule lumen. Thus, this endogenously produced peptide coordinates these two cellular events across the epithelium. Using an NC1-peptide cDNA construct to transfect adult rat testes for its overexpression, NC1-peptide was found to effectively induce germ cell exfoliation, which was associated with a surge and activation of p-rpS6, the downstream signaling protein of mTORC1, and a concomitant down-regulation of p-FAK-Y407 in the testis. In order to define the functional relationship between p-rpS6 and p-FAK-Y407 signaling to confer NC1-peptide the ability to regulate testis function, a phosphomimetic (and thus constitutively active) mutant of p-FAK-Y407, p-FAK-Y407E-MT, was used for its co-transfection with NC1-peptide using Sertoli cells cultured in vitro that mimicked the BTB in vivo. Overexpression of p-FAK-Y407E-MT blocked the effects of NC1-peptide to perturb Sertoli cell BTB function by promoting F-actin and microtubule cytoskeleton function, and downregulated the NC1-peptide mediated induction of p-rpS6 activation. In brief, NC1-peptide is an important endogenously produced biomolecule to regulate BTB dynamics
Bioactive fragments of laminin and collagen chainsāLesson from the testis
Recent studies have shown that the testis is producing several biologically active peptides, namely the F5- and the NC1-peptides from laminin-Ī³3 and collagen Ī±3 (IV) chain, respectively, that promotes blood-testis barrier (BTB) remodeling and also elongated spermatid release at spermiation. Also the LG3/4/5-peptide from laminin-Ī±2 chain also promotes BTB integrity which is likely being used for the assembly of a ānewā BTB behind preleptotene spermatocytes under transport at the immunological barrier. These findings thus provides a new opportunity for investigators to better understand the biology of spermatogenesis. Herein, we briefly summarize these recent findings and provide a critique update and a hypothetical model which can serve as the framework for studies in the years to come