We have performed thermodynamic and neutron scattering measurements on the S=1/2 kagomé lattice antiferromagnet ZnCu3(OH)6Cl2. The susceptibility indicates a Curie-Weiss temperature of theta CW approximately = -300 K; however, no magnetic order is observed down to 50 mK. Inelastic neutron scattering reveals a spectrum of low energy spin excitations with no observable gap down to 0.1 meV. The specific heat at low-T follows a power law temperature dependence. These results suggest that an unusual spin liquid state with essentially gapless excitations is realized in this kagomé lattice system.

Prior to fertilization, oocytes undergo meiotic maturation (cell cycle progression) and ovulation (expulsion from the ovary). To begin the study of these processes in Caenorhabditis elegans, we have defined a time line of germline and somatic events by video microscopy. As the oocyte matures, its nuclear envelope breaks down and its cell cortex rearranges. Immediately thereafter, the oocyte is ovulated by increasing contraction of the myoepithelial gonadal sheath and relaxation of the distal spermatheca. By systematically altering the germ cell contents of the hermaphrodite using mutant strains, we have uncovered evidence of four cell-cell interactions that regulate maturation and ovulation. (1) Both spermatids and spermatozoa induce oocyte maturation. In animals with a feminized germline, maturation is inhibited and oocytes arrest in diakinesis. The introduction of sperm by mating restores maturation. (2) Sperm also directly promote sheath contraction. In animals with a feminized or tumorous germline, contractions are infrequent, whereas in animals with a masculinized germline or with sperm introduced by mating, contractions are frequent. (3 and 4) The maturing oocyte both induces spermathecal dilation and modulates sheath contractions at ovulation; dilation of the distal spermatheca and sharp increases in sheath contraction rates are only observed in the presence of a maturing oocyte.

The syntheses and magnetic susceptibilities of a pure series of rare copper minerals from the atacamite family with general formula ZnxCu4-x(OH)6Cl2 (0

Germ cells complete multiple events to form functional oocytes and sperm. In the Caenorhabditis elegans hermaphrodite, germ cells develop in proximity to the somatic gonad sheath and spermathecal cells. We present evidence from cellular laser ablation studies indicating that cells of the somatic sheath and spermathecal lineages play critical roles in four events of hermaphrodite germline development. (1) Cells of the sheath and spermathecal lineage support germline proliferation; ablation of sheath/spermathecal precursor cells reduces mitotic proliferation. (2) These cells also play a role in the exit of germ cells from the pachytene stage of meiotic prophase and/or gamete differentiation; ablation can result in undifferentiated germ cells arrested in pachytene. (3) Proximal sheath and distal spermatheca cells are required for ovulation of the oocyte. During wild-type ovulation, the mature oocyte is expelled from the gonad arm by contraction of the proximal myoepithelial sheath and dilation of the distal spermatheca. Ablation of these cells traps mature oocytes in the gonad arm where they endomitotically replicate their DNA (the Emo phenotype). (4) Cells of the sheath and spermathecal lineage also appear to promote the male germ cell fate since ablation of one sheath/spermathecal precursor cell can feminize the hermaphrodite germ line. These somatic ablation-induced germline phenotypes demonstrate that the somatic gonad is required for multiple events in C. elegans germline development. Further, these results suggest that soma to germline cell-cell interactions in C. elegans are physiological in character (i.e., contraction during ovulation) as well as regulatory.

No abstract

Multiwalled BN nanotubes are grown from nickel boride catalyst particles by chemical vapor deposition at 1000−1100 °C using borazine, B3N3H6, as the precursor. This precursor is generated in situ from molten salt that forms from mixtures of (NH4)2SO4, NaBH4, and Co3O4 at 300−400 °C. The BN nanotubes have concentric-tube structures, are free of internal closures, have crystalline walls, and exhibit lengths of up to ∼5 μm. The nanotubes often possess bulbous, flag-like, or club-like tip closures. A root-growth mechanism is proposed for the catalyzed process.

The spin-1 2 kagome lattice antiferromagnet herbertsmithite, ZnCu3(OH)6Cl2, is a candidate material for a quantum spin liquid ground state. We show that the magnetic response of this material displays an unusual scaling relation in both the bulk ac susceptibility and the low energy dynamic susceptibility as measured by inelastic neutron scattering. The quantity χT α with α ≃ 0.66 can be expressed as a universal function of H/T or ω/T . This scaling is discussed in relation to similar behavior seen in systems influenced by disorder or by the proximity to a quantum critical point.PACS numbers: 75.40. Gb, 75.50.Ee, 78.70.Nx A continuing challenge in the field of frustrated magnetism is the search for candidate materials which display quantum disordered ground states in two dimensions. In recent years, a great deal of attention has been given to the spin-1 2 nearest-neighbor Heisenberg antiferromagnet on the kagome lattice, consisting of corner sharing triangles. Given the high frustration of the lattice and the strength of quantum fluctuations arising from spin-1 2 moments, this system is a very promising candidate to display novel magnetic ground states, including the "resonating valence bond" (RVB) state proposed by Anderson [1]. A theoretical and numerical consensus has developed that the ground state of this system is not magnetically ordered [2][3][4][5][6][7][8], although the exact ground state is still a matter of some debate. Experimental studies of this system have long been hampered by a lack of suitable materials displaying this motif.The mineral herbertsmithite [9,10], ZnCu 3 (OH) 6 Cl 2 , is believed to be an excellent realization of a spin-1 2 kagome lattice antiferromagnet. The material consists of kagome lattice planes of spin-1 2 Cu 2+ ions. The superexchange interaction between nearest-neighbor spins leads to an antiferromagnetic coupling of J = 17±1 meV. Extensive measurements on powder samples of herbertsmithite have found no evidence of long range magnetic order or spin freezing to temperatures of roughly 50 mK [11][12][13]. Magnetic excitations are effectively gapless, with a Curie-like susceptibility at low temperatures. The magnetic kagome planes are separated by layers of nonmagnetic Zn 2+ ions; however, it has been suggested that there could be some site disorder between the Cu and Zn ions [14,15]. This possible site disorder, with ≈ 5% of the magnetic Cu ions residing on out-of-plane sites, as well as the presence of a Dzyaloshinskii-Moriya (DM) interaction [16], would likely influence the low energy magnetic response.In this Letter we report a dynamic scaling analysis of the susceptibility of herbertsmithite as measured in both the bulk ac susceptibility and the low energy dynamic susceptibility measured by inelastic neutron scattering. In particular, we find that the quantity χT α can be expressed as a universal function in which the energy or field scale is set only by the temperature. This type of scaling behavior, when measured in quantum antiferromagnets [17] and heavy-fermion me...

Although Li-ion batteries have attracted significant interest due to their higher energy density, lack of high rate performance electrode materials and intrinsic safety issues challenge their commercial applications. Herein, we demonstrate a simple photocatalytic reduction method that simultaneously reduces graphene oxide (GO) and anchors (010)-faceted mesoporous bronze-phase titania (TiO2-B) nanosheets to reduced graphene oxide (RGO) through Ti(3+)-C bonds. Formation of Ti(3+)-C bonds during the photocatalytic reduction process was identified using electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) techniques. When cycled between 1-3 V (vs Li(+/0)), these chemically bonded TiO2-B/RGO hybrid nanostructures show significantly higher Li-ion storage capacities and rate capability compared to bare TiO2-B nanosheets and a physically mixed TiO2-B/RGO composite. In addition, 80% of the initial specific (gravimetric) capacity was retained even after 1000 charge-discharge cycles at a high rate of 40C. The improved electrochemical performance of TiO2-B/RGO nanoarchitectures is attributed to the presence of exposed (010) facets, mesoporosity, and efficient interfacial charge transfer between RGO monolayers and TiO2-B nanosheets.