Gate-Tunable Helical Currents in Commensurate Topological Insulator/Graphene Heterostructures

van der Waals heterostructures made from graphene and three-dimensional topological insulators promise very high electron mobilities, a nontrivial spin texture, and a gate-tunability of electronic properties. Such a combination of advantageous electronic characteristics can only be achieved through proximity effects in heterostructures, as graphene lacks a large enough spin-orbit interaction. In turn, the heterostructures are promising candidates for all-electrical control of proximity-induced spin phenomena. Here, we explore epitaxially grown interfaces between graphene and the lattice-matched topological insulator Bi₂Te₂Se. For this heterostructure, spin-orbit coupling proximity has been predicted to impart an anisotropic and electronically tunable spin texture. Polarization-resolved second-harmonic generation, Raman spectroscopy, and time-resolved magneto-optic Kerr microscopy are combined to demonstrate that the atomic interfaces align in a commensurate symmetry with characteristic interlayer vibrations. By polarization-resolved photocurrent measurements, we find a circular photogalvanic effect which is drastically enhanced at the Dirac point of the proximitized graphene. We attribute the peculiar gate-tunability to the proximity-induced interfacial spin structure, which could be exploited for, e.g., spin filters.

Population ageing and women in Kerala State, India

"In this note we examine the ageing of the female population in the State of Kerala, India, in the light of current and future demographic trends as well as the social and economic implications of this process." Consideration is given to the gender gap in mortality, marital status among elderly women, age at marriage, the dependency ratio, and economic status and support for the elderly, including welfare programs.

Variable effects of dengue virus-induced cytotoxic factors on different subpopulations of macrophages

Dengue virus (DV) induces T lymphocytes of the spleen to produce a cytotoxic factor (CF) that induces a subpopulation of macrophages (M phi) to produce a soluble cytotoxin (CF2). Both these factors kill normal lymphoid cells and M phi. The present study was undertaken to investigate the effects of these factors on the I-A-positive and I-A-negative subpopulations of mouse peritoneal M phi. It was observed that CF kills I-A-negative M phi and induces I-A-positive M phi to produce the CF2 that kills both types of cells. However, even when combined together, CF and CF2 do not kill 100% of the M phi. The two-step mechanism involving co-operation between T cells and M phi appears to be biologically economical for maintaining the cytotoxic pathway.

Production of dengue virus-induced macrophage cytotoxin in vivo

We have observed that dengue virus-induced cytotoxic factor (CF) induces peritoneal and splenic macrophages in vitro to produce a cytotoxin (CF2). This study demonstrates also production of CF2 in vivo in DV-infected mice and following inoculation with CF. The cell-type responsible for CF2 production in vivo is the macrophage (M phi) as M phi-depleted mice failed to produce CF2. CF2 activity could not be observed in the serum or peritoneal fluid though it is produced in peritoneal M phi. Once stimulated, CF2 is present for 4 h in M phi. M phi can be restimulated to produce CF2 only after a refractory period of 48 h.

Dengue virus-induced cytotoxic factor induces macrophages to produce a cytotoxin

In our earlier studies we have observed that T lymphocytes of dengue type 2 virus (DV)-infected mouse spleen produce a cytotoxic factor (CF). In the present study it has been observed that CF induces mouse spleen and peritoneal macrophages to produce a cytotoxin (CF2) as has been revealed by DEAE-cellulose chromatography. CF2 is produced by an induction process and is present intracellularly as well as leaking out of the cells. CF2 kills most of the macrophages and some of the T cells, as observed with CF. It appears that CF2 is produced to amplify the effect of CF and/or for cooperative action with CF.

Characterization of the cytotoxin produced by macrophages in response to dengue virus-induced cytotoxic factor

We have observed earlier that dengue type 2 virus-induced cytotoxic factor (CF) induces macrophages to produce a cytotoxin (CF2) which kills mainly the macrophages, some of the T lymphocytes and has no effect on B-lymphocytes of normal mouse spleen. The findings of the present study show that CF2 is heat-labile, trypsin-sensitive and unstable at acid and alkaline pH. It is a low molecular weight product as it is dialysable, non-sedimentable on ultracentrifugation at 103,500 g for 3 h and passes through 0.22 micron Millipore filter. It is adsorbed onto the target normal mouse spleen cells. The properties of CF and CF2 have been compared.

Plasma membrane-acting drugs inhibit the effect of dengue virus-induced cytotoxic factor

Our earlier studies reported that the cytotoxic factor (CF) produced in the spleen of dengue virus type 2-infected mice killed the lymphoid cells of many species of animals and induced normal mouse splenic and peritoneal macrophages to produce a cytotoxin (CF2). In the present study, it has been observed that pretreatment of target cells with cell plasma membrane stabilizers--2,4-dinitrophenol, ouabain and reduced glutathione--prevents the cytotoxicity of CF and blocks the production of CF2, but does not abolish the cytotoxic effect of the latter. CF thus appears to act on target cells through damage to the plasma membrane.

Depressed macrophage functions in dengue virus-infected mice: role of the cytotoxic factor

Dengue virus Type 2 (DV) infection causes immunosuppression in mice. Since macrophages are crucial for immune response, we have studied their functions in this condition and report our findings here. It was observed that in DV-infected mice the phagocytosis of neutral-red and latex particles by splenic and peritoneal-cavity macrophages was significantly reduced (P less than 0.001) from Days 3 to 10 after inoculation. Similarly the migration of splenic and peritoneal macrophages on a glass surface was reduced significantly (P less than 0.001) from Days 4 to 10 after inoculation. Pre-treatment of normal mouse spleen cells with DV-induced cytotoxic factor (CF) inhibited the phagocytic and migratory functions in the same way as observed in DV-infected mice. Higher dilutions of CF (10(-3) and 10(-3.7)) did not kill the cells but affected their functions. It was concluded that macrophage functions are affected by killing and metabolic changes in these cells by DV-induced CF, thus producing immunosuppression.

Inhibition of E-rosette formation and phagocytosis by human blood leucocytes after treatment with the dengue virus-induced cytotoxic factor

We have observed earlier that T lymphocytes of dengue type 2 virus (DV)-infected mouse spleen produce a cytotoxic factor (CF) which kills T lymphocytes and macrophages of the spleen of normal mice or animals of other species. In the present study an effort was made to study the effect of CF treatment on human peripheral blood leucocytes. After treatment with various dilutions of CF at 4 degrees for 1 hr 25%-36% of T lymphocytes lost their capacity to form E rosettes and 25%-36% of monocytes lost their phagocytic function. Cytotoxic-factor treatment had no effect on formation of EAC rosettes by B lymphocytes and the phagocytic functions of polymorphonuclear cells. Pretreatment of cells with 2,4 dinitrophenol, reduced glutathione or ouabain, which act on the cell membrane, inhibited the effect of CF on E-rosette formation and phagocytosis. This indicated that CF acts by inducing changes in the cell membrane. It is likely that production of a similar factor in DV-infected humans is responsible for similar alterations observed in their blood.

Marked preference for female sterilization in a semirural squatter settlement

The following article analyzes the reasons very poor semirural women in South India choose sterilization as a means of birth control. The women, who work for minimal wages in a narrowing job market and whose children have little hope for jobs or land marriages, are choosing to be sterilized after two or three births. Among their limited range of contraceptive choices, female sterilization in the nearby hospital where women go for deliveries and abortion is perceived by them to be the most advantageous in terms of the cost of medicines and transportation and time away from jobs. The article illustrates the centrality of economic factors in low-income women's family planning decisions.