3,780 research outputs found
Toward Perfection: Kapellasite, Cu3Zn(OH)6Cl2, a New Model S = 1/2 Kagome Antiferromagnet
The search for the resonating valence bond (RVB) state continues to underpin
many areas of condensed matter research. The RVB is made from the dimerisation
of spins on different sites into fluctuating singlets, and was proposed by
Anderson to be the reference state from which the transition to BCS
superconductivity occurs. Little is known about the state experimentally, due
to the scarcity of model materials. Theoretical work has put forward the S =
1/2 kagome antiferromagnet (KAFM) as a good candidate for the realization of
the RVB state. In this paper we introduce a new model system, the S = 1/2 KAFM
Kapellasite, Cu3Zn(OH)6Cl2. We show that its crystal structure is a good
approximation to a 2-dimensional kagome antiferromagnet and that susceptibility
data indicate a collapse of the magnetic moment below T = 25 K that is
compatible with the spins condensing into the non-magnetic RVB state.Comment: Communication, 3 pages, 3 figure
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HCMV Antivirals and Strategies to Target the Latent Reservoir.
Human cytomegalovirus (HCMV) is a ubiquitous human herpesvirus. In healthy people, primary infection is generally asymptomatic, and the virus can go on to establish lifelong latency in cells of the myeloid lineage. However, HCMV often causes severe disease in the immunosuppressed: transplant recipients and people living with AIDS, and also in the immunonaive foetus. At present, there are several antiviral drugs licensed to control HCMV disease. However, these are all faced with problems of poor bioavailability, toxicity and rapidly emerging viral resistance. Furthermore, none of them are capable of fully clearing the virus from the host, as they do not target latent infection. Consequently, reactivation from latency is a significant source of disease, and there remains an unmet need for treatments that also target latent infection. This review briefly summarises the most common HCMV antivirals used in clinic at present and discusses current research into targeting the latent HCMV reservoir
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Bromodomain Inhibitors as Therapeutics for Herpesvirus-Related Disease: All BETs Are Off?
Although the ubiquitous human herpesviruses (HHVs) are rarely associated with serious disease of the healthy host, primary infection and reactivation in immunocompromised individuals can lead to significant morbidity and, in some cases, mortality. Effective drugs are available for clinical treatment, however resistance is on the rise such that new anti-viral targets, as well as novel clinical treatment strategies, are required. A promising area of development and pre-clinical research is that of inhibitors of epigenetic modifying proteins that control both cellular functions and the viral life cycle. Here, we briefly outline the interaction of the host bromo- and extra-terminal domain (BET) proteins during different stages of the HHVs' life cycles while giving a full overview of the published work using BET bromodomain inhibitors (BRDis) during HHV infections. Furthermore, we provide evidence that small molecule inhibitors targeting the host BET proteins, and BRD4 in particular, have the potential for therapeutic intervention of HHV-associated disease
Prototype Backscatter Moessbauer Spectrometer for Measurement of Martian Surface Mineralogy
We have designed and successfully tested a prototype of a backscatter Moessbauer spectrometer (BaMS) targeted for use on the Martian surface to (1) determine oxidation states of iron, and (2) identify and determine relative abundances of iron-bearing mineralogies. No sample preparation is required to perform measurements; it is only necessary to bring sample and instrument into physical contact. The prototype meets our projected specification for a flight instrument in terms of mass, power, and volume. A Moessbauer spectrometer on the Martian surface would provide wide variety of information about the current state of the Martian surface, and this information is described
On the Nature of Soft X-ray Weak Quasi-Stellar Objects
Recent studies of QSOs with ROSAT suggest the existence of a significant
population of Soft X-ray Weak QSOs (SXW QSOs) where the soft X-ray flux is ~
10-30 times smaller than in typical QSOs. As a first step in a systematic study
of these objects, we establish a well-defined sample of SXW QSOs which includes
all alpha_ox<=-2 QSOs from the Boroson & Green (1992) sample of 87 BQS QSOs.
SXW QSOs comprise about 11% of this optically selected QSO sample. From an
analysis of CIV absorption in the 55 BG92 QSOs with available CIV data, we find
a remarkably strong correlation between alpha_ox and the CIV absorption
equivalent width. This correlation suggests that absorption is the primary
cause of soft X-ray weakness in QSOs, and it reveals a continuum of absorption
properties connecting unabsorbed QSOs, X-ray warm absorber QSOs, SXW QSOs and
BAL QSOs. From a practical point of view, our correlation demonstrates that
selection by soft X-ray weakness is an effective (>=80% successful) and
observationally inexpensive way to find low-redshift QSOs with strong and
interesting ultraviolet absorption. We have also identified several notable
differences between the optical emission-line properties of SXW QSOs and those
of the other BG92 QSOs. SXW QSOs show systematically low [O III] luminosities
as well as distinctive H-beta profiles. They tend to lie toward the weak-[O
III] end of BG92 eigenvector 1, as do many low-ionization BAL QSOs. Unabsorbed
Seyferts and QSOs with similar values of eigenvector 1 have been suggested to
have extreme values of a primary physical parameter, perhaps mass accretion
rate relative to the Eddington rate (M-dot/M-dot_{Edd}). If these suggestions
are correct, it is likely that SXW QSOs also tend to have generally high values
of (M-dot/M-dot_{Edd}). (Abridged)Comment: 34 pages, ApJ accepted, also available from
http://www.astro.psu.edu/users/niel/papers/papers.htm
The immunology of human cytomegalovirus latency: could latent infection be cleared by novel immunotherapeutic strategies?
While the host immune response following primary human cytomegalovirus (HCMV) infection is generally effective at stopping virus replication and dissemination, virus is never cleared by the host and like all herpesviruses, persists for life. At least in part, this persistence is known to be facilitated by the ability of HCMV to establish latency in myeloid cells in which infection is essentially silent with, importantly, a total lack of new virus production. However, although the viral transcription programme during latency is much suppressed, a number of viral genes are expressed during latent infection at the protein level and many of these have been shown to have profound effects on the latent cell and its environment. Intriguingly, many of these latency-associated genes are also expressed during lytic infection. Therefore, why the same potent host immune responses generated during lytic infection to these viral gene products are not recognized during latency, thereby allowing clearance of latently infected cells, is far from clear. Reactivation from latency is also a major cause of HCMV-mediated disease, particularly in the immune compromised and immune naive, and is also likely to be a major source of virus in chronic subclinical HCMV infection which has been suggested to be associated with long-term diseases such as atherosclerosis and some neoplasias. Consequently, understanding latency and why latently infected cells appear to be immunoprivileged is crucial for an understanding of the pathogenesis of HCMV and may help to design strategies to eliminate latent virus reservoirs, at least in certain clinical settings.This work was funded by British Medical Research Council Grant JS and MW - G0701279 and MR/K021087/1 and supported by the NIHR Cambridge BRC Cell Phenotyping hub.This is the accepted manuscript. The final version is available from the publisher at http://www.nature.com/cmi/journal/vaop/ncurrent/full/cmi201475a.html
VLA H92 Alpha and H53 Alpha Radio Recombination Line Observations of M82
We present high angular resolution (0.6'') observations made with the VLA of
the radio continuum at 8.3 and 43 GHz as well as H92 Alpha and H53 Alpha radio
recombination lines from the nearby (3 Mpc) starburst galaxy M82. In the
continuum we report 19 newly identified sources at 8.3 GHz and 5 at 43 GHz that
were unknown previously. The spatial distribution of the H92 Alpha line is
inhomogeneous; we identify 27 features. The line and continuum emission are
modeled using a collection of HII regions at different distances from the
nucleus assuming a single-density component and two-density components. The
high-density component has a density of 4 X 10^{4} cm^{-3}. However, the bulk
of the ionization is in regions with densities which are typically a factor 10
lower. The gas kinematics, using the H92 Alpha line, confirms the presence of
steep velocity gradient (26 km s^{-1} arcsec^{-1}) in the nuclear region. As
this steep gradient is observed not only on the major axis but also at large
distances along a band of PA of 150 degrees, the interpretation in terms of x2
orbits elongated along the minor axis of the bar, which would be observed at an
angle close to the inclination of the main disk, seems inadequate. Ad-hoc
radial motions must be introduced to reproduce the pattern of the velocity
field. Different families of orbits are indicated as we detect a signature in
the kinematics at the transition between the two plateaus observed in the NIR
light distribution. The H92 Alpha line also reveals the base of the outflow
where the injection towards the halo on the Northern side occurs. The
kinematical pattern suggests a connection between the gas flowing in the plane
of M82 towards the center; this behavior most likely originates due to the
presence of a bar and the outflow out of the plane.Comment: 45 pages, 11 figures and 6 tables. Accepted for publication in Ap
Moessbauer Spectroscopy for Lunar Resource Assessment: Measurement of Mineralogy and Soil Maturity
First-order assessment of lunar soil as a resource includes measurement of its mineralogy and maturity. Soils in which the mineral ilmenite is present in high concentrations are desirable feedstock for the production of oxygen at a lunar base. The maturity of lunar soils is a measure of their relative residence time in the upper 1 mm of the lunar surface. Increasing maturity implies increasing load of solar wind species (e.g., N, H, and He-3), decreasing mean grain size, and increasing glass content. All these physicochemical properties that vary in a regular way with maturity are important parameters for assessing lunar soil as a resource. For example, He-3 can be extracted and potentially used for nuclear fusion. A commonly used index for lunar soil maturity is I(sub s)/FeO, which is the concentration of fine-grained metal determined by ferromagnetic resonance (I(sub s)) normalized to the total iron content (as FeO). I(sub s)/FeO has been measured for virtually every soil returned by the Apollo and Luna missions to the Moon. Because the technique is sensitive to both oxidation state and mineralogy, iron Moessbauer spectroscopy (FeMS) is a viable technique for in situ lunar resource assessment. Its utility for mineralogy is apparent from examination of published FeMS data for lunar samples. From the data published, it can be inferred that FeMS data can also be used to determine soil maturity. The use of FeMS to determine mineralogy and maturity and progress on development of a FeMS instrument for lunar surface use are discussed
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