364 research outputs found
Competition and coexistence of bond and charge orders in (TMTTF)2AsF6
(TMTTF)2AsF6 undergoes two phase transitions upon cooling from 300 K. At
Tco=103 K a charge-ordering (CO) occurs, and at Tsp(B=9 T)=11 K the material
undergoes a spin-Peierls (SP) transition. Within the intermediate, CO phase,
the charge disproportionation ratio is found to be at least 3:1 from carbon-13
NMR 1/T1 measurements on spin-labeled samples. Above Tsp, up to about 3Tsp,
1/T1 is independent of temperature, indicative of low-dimensional magnetic
correlations. With the application of about 0.15 GPa pressure, Tsp increases
substantially, while Tco is rapidly suppressed, demonstrating that the two
orders are competing. The experiments are compared to results obtained from
calculations on the 1D extended Peierls-Hubbard model.Comment: 4 pages, 5 figure
Comparison of ixekizumab with ustekinumab in moderate-to-severe psoriasis: 24-week results from IXORA-S, a phase III study
Background It has been shown that the interleukin (IL)-23/IL-17 axis is critical in the pathogenesis of psoriasis. Objectives To present the primary end point (week 12) and safety and efficacy data up to week 24 from a head-to-head trial (IXORA-S) of the IL-17A inhibitor ixekizumab (IXE) vs. the IL-12/23 inhibitor ustekinumab (UST). Methods Randomized patients received IXE (160-mg starting dose, then 80 mg every 2 weeks for 12 weeks, then 80 mg every 4 weeks, n = 136) or UST (45 mg or 90 mg weight-based dosing per label, n = 166). The primary end point was the proportion of patients reaching ≥ 90% Psoriasis Area and Severity Index improvement (PASI 90). Hommel-adjusted key secondary end points at week 12 included PASI 75, PASI 100, static Physician's Global Assessment (sPGA) score of 0 or 1, sPGA score of 0, Dermatology Life Quality Index (DLQI) score of 0 or 1, ≥ 4-point reduction on the itch numerical rating scale (NRS) and changes in itch NRS and skin pain visual analogue scale. Results At week 12, IXE (n = 99, 72 8%) was superior to UST (n = 70, 42 2%) in PASI 90 response (response difference 32 1%, 97 5% confidence interval 19 8 44 5%, P < 0 001). Response rates for PASI 75, PASI 100 and sPGA (0,1) were significantly higher for IXE than for UST (adjusted P < 0 05). At week 24, IXEtreated patients had significantly higher response rates than UST-treated patients for PASI, sPGA and DLQI (unadjusted P < 0 05). No deaths were reported, and the treatments did not differ with regard to overall incidences of adverse events (P = 0 299). Conclusions The superior efficacy of IXE demonstrated at week 12 persisted up to week 24. The safety profiles were consistent with those previously reported for both treatments. peerReviewe
Automated Coronal Hole Detection using Local Intensity Thresholding Techniques
We identify coronal holes using a histogram-based intensity thresholding
technique and compare their properties to fast solar wind streams at three
different points in the heliosphere. The thresholding technique was tested on
EUV and X-ray images obtained using instruments onboard STEREO, SOHO and
Hinode. The full-disk images were transformed into Lambert equal-area
projection maps and partitioned into a series of overlapping sub-images from
which local histograms were extracted. The histograms were used to determine
the threshold for the low intensity regions, which were then classified as
coronal holes or filaments using magnetograms from the SOHO/MDI. For all three
instruments, the local thresholding algorithm was found to successfully
determine coronal hole boundaries in a consistent manner. Coronal hole
properties extracted using the segmentation algorithm were then compared with
in situ measurements of the solar wind at 1 AU from ACE and STEREO. Our results
indicate that flux tubes rooted in coronal holes expand super-radially within 1
AU and that larger (smaller) coronal holes result in longer (shorter) duration
high-speed solar wind streams
A 1400-years flood frequency reconstruction for the Basque country (N Spain): Integrating geological, historical and instrumental datasets
We present the first reconstruction of past flood events variability in the Basque Country and Western Ebro Basin (Northern Spain) integrating instrumental hydrological datasets (last 20 years), documentary archives (last 700 years) and Lake Arreo (655 m a.s.l.) sedimentary paleoflood record (last 1400 years). In this lake, allochthonous coarse and fine detrital layers (CDL and FDL respectively) intercalated within endogenic laminites were identified and interpreted as high- and moderate-energy flood events. The interplay between human activities and hydroclimate variability has controlled the deposition of these flood layers. Gauged data for the last 20 years suggest that floods are typically generated by heavy rainfall events on saturated soils after several days of continuous rainfall. These events occur mostly during the cold season (Oct–May). The reconstructed frequency of high-magnitude flood events from the lake record is coherent with the historical cold-season floods from Basque rivers. The lowest flood frequency took place during the 6–7th and 10–15th centuries, while higher flood frequency occurred during the 8–9th centuries and the last 500 years. Fluvial and lacustrine paleoflood records and documentary evidence show abrupt and large increases in extreme flood frequency during the termination of the Little Ice Age (1830–1870 CE) and mid to late 20th century, both periods of Rapid Climate Change (RCC). The significant increase in flood frequency observed during RCC suggests that a similar pattern could be expected in the near future with the ongoing global warming.</p
A new measurement of direct CP violation in two pion decays of the neutral kaon
The NA48 experiment at CERN has performed a new measurement of direct CP
violation, based on data taken in 1997 by simultaneously collecting K_L and K_S
decays into pi0pi0 and pi+pi-. The result for the CP violating parameter
Re(epsilon'/epsilon) is (18.5 +/- 4.5(stat)} +/- 5.8 (syst))x10^{-4}.Comment: 18 pages, 6 figure
Anisotropy of the orbital methods and the magnetic dipole term in : An {\it ab-initio} studt
A systematic study is performed by the {\it ab-initio} density functional
theory of the anisotropy of the orbital moments in bulk . Two different band-structure techniques are
used (FLAPW and LMTO-ASA), and the electronic correlations are treated by the
local-spin-density approximation (LSDA), the LSDA+ orbital polarization method,
and the LSDA+ method. The calculated anisotropies of are
very large compared to Fe, Ni and Co but still a factor of 5 and 2 smaller than
the anisotropies obtained from a recently suggested analysis of the X-ray
magnetic circular dichroism spectra for a thick layer of
Physics of Solar Prominences: I - Spectral Diagnostics and Non-LTE Modelling
This review paper outlines background information and covers recent advances
made via the analysis of spectra and images of prominence plasma and the
increased sophistication of non-LTE (ie when there is a departure from Local
Thermodynamic Equilibrium) radiative transfer models. We first describe the
spectral inversion techniques that have been used to infer the plasma
parameters important for the general properties of the prominence plasma in
both its cool core and the hotter prominence-corona transition region. We also
review studies devoted to the observation of bulk motions of the prominence
plasma and to the determination of prominence mass. However, a simple inversion
of spectroscopic data usually fails when the lines become optically thick at
certain wavelengths. Therefore, complex non-LTE models become necessary. We
thus present the basics of non-LTE radiative transfer theory and the associated
multi-level radiative transfer problems. The main results of one- and
two-dimensional models of the prominences and their fine-structures are
presented. We then discuss the energy balance in various prominence models.
Finally, we outline the outstanding observational and theoretical questions,
and the directions for future progress in our understanding of solar
prominences.Comment: 96 pages, 37 figures, Space Science Reviews. Some figures may have a
better resolution in the published version. New version reflects minor
changes brought after proof editin
The Science of Sungrazers, Sunskirters, and Other Near-Sun Comets
This review addresses our current understanding of comets that venture close to the Sun, and are hence exposed to much more extreme conditions than comets that are typically studied from Earth. The extreme solar heating and plasma environments that these objects encounter change many aspects of their behaviour, thus yielding valuable information on both the comets themselves that complements other data we have on primitive solar system bodies, as well as on the near-solar environment which they traverse. We propose clear definitions for these comets: We use the term near-Sun comets to encompass all objects that pass sunward of the perihelion distance of planet Mercury (0.307 AU). Sunskirters are defined as objects that pass within 33 solar radii of the Sun’s centre, equal to half of Mercury’s perihelion distance, and the commonly-used phrase sungrazers to be objects that reach perihelion within 3.45 solar radii, i.e. the fluid Roche limit. Finally, comets with orbits that intersect the solar photosphere are termed sundivers. We summarize past studies of these objects, as well as the instruments and facilities used to study them, including space-based platforms that have led to a recent revolution in the quantity and quality of relevant observations. Relevant comet populations are described, including the Kreutz, Marsden, Kracht, and Meyer groups, near-Sun asteroids, and a brief discussion of their origins. The importance of light curves and the clues they provide on cometary composition are emphasized, together with what information has been gleaned about nucleus parameters, including the sizes and masses of objects and their families, and their tensile strengths. The physical processes occurring at these objects are considered in some detail, including the disruption of nuclei, sublimation, and ionisation, and we consider the mass, momentum, and energy loss of comets in the corona and those that venture to lower altitudes. The different components of comae and tails are described, including dust, neutral and ionised gases, their chemical reactions, and their contributions to the near-Sun environment. Comet-solar wind interactions are discussed, including the use of comets as probes of solar wind and coronal conditions in their vicinities. We address the relevance of work on comets near the Sun to similar objects orbiting other stars, and conclude with a discussion of future directions for the field and the planned ground- and space-based facilities that will allow us to address those science topics
Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy
We review HB stars in a broad astrophysical context, including both variable
and non-variable stars. A reassessment of the Oosterhoff dichotomy is
presented, which provides unprecedented detail regarding its origin and
systematics. We show that the Oosterhoff dichotomy and the distribution of
globular clusters (GCs) in the HB morphology-metallicity plane both exclude,
with high statistical significance, the possibility that the Galactic halo may
have formed from the accretion of dwarf galaxies resembling present-day Milky
Way satellites such as Fornax, Sagittarius, and the LMC. A rediscussion of the
second-parameter problem is presented. A technique is proposed to estimate the
HB types of extragalactic GCs on the basis of integrated far-UV photometry. The
relationship between the absolute V magnitude of the HB at the RR Lyrae level
and metallicity, as obtained on the basis of trigonometric parallax
measurements for the star RR Lyrae, is also revisited, giving a distance
modulus to the LMC of (m-M)_0 = 18.44+/-0.11. RR Lyrae period change rates are
studied. Finally, the conductive opacities used in evolutionary calculations of
low-mass stars are investigated. [ABRIDGED]Comment: 56 pages, 22 figures. Invited review, to appear in Astrophysics and
Space Scienc
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