Long-range ferromagnetism of Mn12 acetate single-molecule magnets under a transverse magnetic field

We use neutron diffraction to probe the magnetization components of a crystal of Mn12 single-molecule magnets. Each of these molecules behaves, at low temperatures, as a nanomagnet with spin S = 10 and strong anisotropy along the crystallographic c axis. Application of a magnetic field perpendicular to c induces quantum tunneling between opposite spin orientations, enabling the spins to attain thermal equilibrium. Below approximately 0.9 K, intermolecular interactions turn this equilibrium state into a ferromagnetically ordered phase. However, long range ferromagnetic correlations nearly disappear for fields larger 5.5 T, possibly suggesting the existence of a quantum critical point.Comment: 4 pages, 4 figure

Broad N2H+ emission towards the protostellar shock L1157-B1

We present the first detection of N2H+ towards a low-mass protostellar outflow, namely the L1157-B1 shock, at about 0.1 pc from the protostellar cocoon. The detection was obtained with the IRAM 30-m antenna. We observed emission at 93 GHz due to the J = 1-0 hyperfine lines. The analysis of the emission coupled with the HIFI CHESS multiline CO observations leads to the conclusion that the observed N2H+(1-0) line originates from the dense (> 10^5 cm-3) gas associated with the large (20-25 arcsec) cavities opened by the protostellar wind. We find a N2H+ column density of few 10^12 cm-2 corresponding to an abundance of (2-8) 10^-9. The N2H+ abundance can be matched by a model of quiescent gas evolved for more than 10^4 yr, i.e. for more than the shock kinematical age (about 2000 yr). Modelling of C-shocks confirms that the abundance of N2H+ is not increased by the passage of the shock. In summary, N2H+ is a fossil record of the pre-shock gas, formed when the density of the gas was around 10^4 cm-3, and then further compressed and accelerated by the shock.Comment: ApJ, in pres

Composition of Kinetic Momenta: The U_q(sl(2)) case

The tensor products of (restricted and unrestricted) finite dimensional irreducible representations of \uq are considered for $q$ a root of unity. They are decomposed into direct sums of irreducible and/or indecomposable representations.Comment: 27 pages, harvmac and tables macros needed, minor TeXnical revision to allow automatic TeXin

Targeted Community Merging provides an efficient comparison between collaboration clusters and departmental partitions

Community detection theory is vital for the structural analysis of many types of complex networks, especially for human-like collaboration networks. In this work, we present a new community detection algorithm, the Targeted Community Merging algorithm, based on the well-known Girvan–Newman algorithm, which allows obtaining community partitions with high values of modularity and a small number of communities. We then perform an analysis and comparison between the departmental and community structure of scientific collaboration networks within the University of Zaragoza. Thus, we draw valuable conclusions from the inter- and intra-departmental collaboration structure that could be useful to take decisions on an eventual departmental restructuring

Diagnosing shock temperature with NH3_3 and H2_2O profiles

In a previous study of the L1157 B1 shocked cavity, a comparison between NH$_3$(1$_0$-$0_0$) and H$_2$O(1$_{\rm 10}$--1$_{\rm 01}$) transitions showed a striking difference in the profiles, with H$_2$O emitting at definitely higher velocities. This behaviour was explained as a result of the high-temperature gas-phase chemistry occurring in the postshock gas in the B1 cavity of this outflow. If the differences in behaviour between ammonia and water are indeed a consequence of the high gas temperatures reached during the passage of a shock, then one should find such differences to be ubiquitous among chemically rich outflows. In order to determine whether the difference in profiles observed between NH$_3$ and H$_2$O is unique to L1157 or a common characteristic of chemically rich outflows, we have performed Herschel-HIFI observations of the NH$_3$(1$_0$-0$_0$) line at 572.5 GHz in a sample of 8 bright low-mass outflow spots already observed in the H$_2$O(1$_{\rm 10}$--1$_{\rm 01}$) line within the WISH KP. We detected the ammonia emission at high-velocities at most of the outflows positions. In all cases, the water emission reaches higher velocities than NH$_3$, proving that this behaviour is not exclusive of the L1157-B1 position. Comparisons with a gas-grain chemical and shock model confirms, for this larger sample, that the behaviour of ammonia is determined principally by the temperature of the gas.Comment: Accepted for publication in the Monthly Notices of the Royal Astronomical Societ

Kinematics of the H2O masers at the centre of the PN K3-35

We have studied the kinematics traced by the water masers located at the centre of the planetary nebula (PN) K3-35, using data from previous Very Large Array (VLA) observations. An analysis of the spatial distribution and line-of-sight velocities of the maser spots allows us to identify typical patterns of a rotating and expanding ring in the position-velocity diagrams, according to our kinematical model. We find that the distribution of the masers is compatible with tracing a circular ring with a ~0.021 arcsec (~100 AU) radius, observed with an inclination angle with respect to the line of sight of 55 degrees. We derive expansion and rotation velocities of 1.4 and 3.1 km/s, respectively. The orientation of the ring projected on the plane of the sky, at PA 158 degrees, is almost orthogonal to the direction of the innermost region of the jet observed in K3-35, suggesting the presence of a disc or torus that may be related to the collimation of the outflow.Comment: 7 pages, 4 figures, 2 tables. Accepted by MNRA

Comparison of the viscoelastic properties of human abdominal and breast adipose tissue and its incidence on breast reconstruction surgery. A pilot study

Background: Breast cancer is the leading malignant tumor in women in the world. Reconstruction after mastectomy plays a key role in the physical and psychological recuperation, being the abdominal skin and adipose tissue the best current option for the DIEP surgery. The aim of the surgery is to obtain a reconstructed breast which looks and behaves naturally. Therefore, it would be useful to characterize the mechanical behaviour of the adipose tissue in the abdomen and breast to compare their mechanical properties, also investigating possible regional differences. Methods: Experimental tests have been carried out in breast and abdominal adipose tissue samples, obtaining their viscoelastic properties. The specimens have been subjected to uniaxial compression relaxation tests and a mechanical behaviour model has been fitted to the experimental curves. Afterwards, statistical analyses have been used to detect differences between different individuals' abdominal fat tissue and finally between different areas of the same individual's breast and abdominal adipose tissue. Findings: Several conclusions could be extracted from the results: 1) inter-individual differences may exist in the abdominal adipose tissue; 2) the breast fat could be regarded as a unique tissue from the mechanical point of view; 3) significant differences were detected between the superficial breast and all the locations of the abdomen, except for the superficial lateral one and 4) the mechanical properties of the abdominal adipose tissue seem to change with the depth. These conclusions can be of great value for DIEP surgeries and other surgeries in which the adipose tissue is involved.Ministerio de Economía y Competitividad DPI2011-2808

The CHESS survey of the L1157-B1 bow-shock: high and low excitation water vapor

Molecular outflows powered by young protostars strongly affect the kinematics and chemistry of the natal molecular cloud through strong shocks resulting in substantial modifications of the abundance of several species. As part of the "Chemical Herschel Surveys of Star forming regions" guaranteed time key program, we aim at investigating the physical and chemical conditions of H20 in the brightest shock region B1 of the L1157 molecular outflow. We observed several ortho- and para-H2O transitions using HIFI and PACS instruments on board Herschel, providing a detailed picture of the kinematics and spatial distribution of the gas. We performed a LVG analysis to derive the physical conditions of H2O shocked material, and ultimately obtain its abundance. We detected 13 H2O lines probing a wide range of excitation conditions. PACS maps reveal that H2O traces weak and extended emission associated with the outflow identified also with HIFI in the o-H2O line at 556.9 GHz, and a compact (~10") bright, higher-excitation region. The LVG analysis of H2O lines in the bow-shock show the presence of two gas components with different excitation conditions: a warm (Tkin~200-300 K) and dense (n(H2)~(1-3)x10^6 cm-3) component with an assumed extent of 10" and a compact (~2"-5") and hot, tenuous (Tkin~900-1400 K, n(H2)~10^3-10^4 cm-3) gas component, which is needed to account for the line fluxes of high Eu transitions. The fractional abundance of the warm and hot H2O gas components is estimated to be (0.7-2)x10^{-6} and (1-3)x10^{-4}, respectively. Finally, we identified an additional component in absorption in the HIFI spectra of H2O lines connecting with the ground state level, probably arising from the photodesorption of icy mantles of a water-enriched layer at the edges of the cloud.Comment: Accepted for publication in A&A. 12 pages, 9 figures, 4 table