A Deep WSRT 1.4 GHz Radio Survey of the Spitzer Space Telescope FLSv Region

The First Look Survey (FLS) is the first scientific product to emerge from the Spitzer Space Telescope. A small region of this field (the verification strip) has been imaged very deeply, permitting the detection of cosmologically distant sources. We present Westerbork Synthesis Radio Telescope (WSRT) observations of this region, encompassing a ~1 sq. deg field, centred on the verification strip (J2000 RA=17:17:00.00, DEC=59:45:00.000). The radio images reach a noise level of ~ 8.5 microJy/beam - the deepest WSRT image made to date. We summarise here the first results from the project, and present the final mosaic image, together with a list of detected sources. The effect of source confusion on the position, size and flux density of the faintest sources in the source catalogue are also addressed. The results of a serendipitous search for HI emission in the field are also presented. Using a subset of the data, we clearly detect HI emission associated with four galaxies in the central region of the FLSv. These are identified with nearby, massive galaxies.Comment: 9 pages, 6 figures (fig.3 in a separate gif file). Accepted for publication in A&A. The full paper and the related material can be downloaded from http://www.astron.nl/wsrt/WSRTsurveys/WFLS

Bound states of magnons in the S=1/2 quantum spin ladder

We study the excitation spectrum of the two-leg antiferromagnetic S=1/2 Heisenberg ladder. Our approach is based on the description of the excitations as triplets above a strong-coupling singlet ground state. The quasiparticle spectrum is calculated by treating the excitations as a dilute Bose gas with infinite on-site repulsion. We find singlet (S=0) and triplet (S=1) two-particle bound states of the elementary triplets. We argue that bound states generally exist in any dimerized quantum spin model.Comment: 4 REVTeX pages, 4 Postscript figure

Leveraging agrobiodiversity to create sustainable food systems for healthier diets

The current ways that planetary resources are used to produce and consume food are raising significant concerns about the impact on nutrition, health and sustainability. A major reorientation of our food systems is needed in terms of both activities and governance. This paper describes the important contributions agricultural biodiversity makes achieving healthy diets and sustainable food systems and highlights a number of key actions needed to maximize those contributions. Dietary factors are the number one risk factor in the global burden of disease. At the same time, many of the ways in which food systems operate, from production to sales and consumption, are causing significant environmental damage, including loss of biodiversity and of the beneficial services that biodiversity in ecosystems provides to humanity. This paper argues that focusing on increasing agricultural biodiversity in landscapes, food systems and diets is an important part of the solution to creating healthier diets from sustainable food systems. For instance, a healthy diet should be based on whole grains, fruit, vegetables, legumes, nuts and seeds, and be limited in added sugar and sodium. Agrobiodiversity can ensure these essential ingredients are present in our food system, and so support healthy diets. In terms of increased sustainability of food systems, agricultural biodiversity can boost yields, provide pollination services and pest and disease control, reduce the need for inorganic fertilizers and synthetic pesticides, and provide protection to natural habitats. Agrobiodiversity can also contribute to breeding of crops and animals that are more capable of coping with climate change. Good governance is key to achieving positive outcomes from promotion of agrobiodiversity. Food systems arise from complex agronomic, economic, political, institutional and social interrelationships. Good governance must drive the enabling environment that influences multiple actors operating in these systems and the actions they can take that will impact on the sustainability of food systems and the creation of healthy diets. Promoting agricultural biodiversity can be a practical investment for healthier diets through four main avenues: local and more nutritious value chains; public or institutional procurement; increased availability of fruits and vegetables; and appropriate policy incentives and coherence for diversification of production and consumption. We use examples from a number of contexts to illustrate potential actions that other countries may follow

Magnetic Properties of (VO)_2P_2O_7 from Frustrated Interchain Coupling

Neutron-scattering experiments on (VO)_2P_2O_7 reveal both a gapped magnon dispersion and an unexpected, low-lying second mode. The proximity and intensity of these modes suggest a frustrated coupling between the alternating spin chains. We deduce the minimal model containing such a frustration, and show that it gives an excellent account of the magnon dispersion, static susceptibility and electron spin resonance absorption. We consider two-magnon states which bind due to frustration, and demonstrate that these may provide a consistent explanation for the second mode.Comment: RevTeX, 5 pages, 6 figures, compressed from first versio

High-z radio starbursts host obscured X-ray AGN

We use Virtual Observatory methods to investigate the association between radio and X-ray emission at high redshifts. Fifty-five of the 92 HDF(N) sources resolved by combining MERLIN+VLA data were detected by Chandra, of which 18 are hard enough and bright enough to be obscured AGN. The high-z population of microJy radio sources is dominated by starbursts an order of magnitude more active and more extended than any found at z<1 and at least a quarter of these simultaneously host highly X-ray-luminous obscured AGN.Comment: 4 pages, 2 figures, To appear in the proceedings of 'At the Edge of the Universe' (9-13 October 2006, Sintra, Portugal

Magnetic properties of (VO)_2P_2O_7: two-plane structure and spin-phonon interactions

Detailed experiments on single-crystal (VO)_2P_2O_7 continue to reveal new and unexpected features. We show that a model composed of two, independent planes of spin chains with frustrated magnetic coupling is consistent with nuclear magnetic resonance and inelastic neutron scattering measurements. The pivotal role of PO_4 groups in mediating intrachain exchange interactions explains both the presence of two chain types and their extreme sensitivity to certain lattice vibrations, which results in the strong magnetoelastic coupling observed by light scattering. We compute the respective modifications of the spin and phonon dynamics due to this coupling, and illustrate their observable consequences on the phonon frequencies, magnon dispersions, static susceptibility and specific heat.Comment: 10 pages, 9 figure

Constraining H0 from Chandra Observations of Q0957+561

We report the detection of the lens cluster of the gravitational lens (GL) system Q0957+561 from a deep observation with the Advanced CCD Imaging Spectrometer on-board the Chandra X-ray Observatory. Intracluster X-ray emission is found to be centered 4.3 +/- 1.3 arcsec east and 3.5(-0.6,+1.3) arcsec north of image B, nearer than previous estimates. Its spectrum can be modeled well with a thermal plasma model consistent with the emission originating from a cluster at a redshift of 0.36. Our best-fit estimates of the cluster temperature of T_e = 2.09(-0.54,+0.83) keV (90 percent confidence) and mass distribution of the cluster are used to derive the convergence parameter kappa, the ratio of the cluster surface mass density to the critical density required for lensing. We estimate the convergence parameter at the location of the lensed images A and B to be kappa_A = 0.22(+0.14,-0.07) and kappa_B = 0.21(+0.12,-0.07), respectively (90 percent confidence levels). The observed cluster center, mass distribution and convergence parameter kappa provide additional constraints to lens models of this system. Our new results break a mass-sheet degeneracy in GL models of this system and provide better constraints of ~ 29 percent (90 percent confidence levels) on the Hubble constant. We also present results from the detection of the most distant X-ray jet (z = 1.41) detected to date. The jet extends approximately 8 arcsec NE of image A and three knots are resolved along the X-ray jet with flux densities decreasing with distance from the core. The observed radio and optical flux densities of the knots are fitted well with a synchrotron model and the X-ray emission is modeled well with inverse Compton scattering of Cosmic Microwave Background photons by synchrotron-emitting electrons in the jet.Comment: 18 pages, includes 7 figures, Accepted for publication in Ap

Level densities and γ\gamma-ray strength functions in 170,171,172^{170,171,172}Yb

Level densities and radiative strength functions in $^{171}$Yb and $^{170}$Yb nuclei have been measured using the $^{171}$Yb($^3$He,$^3$He$^\prime\gamma$)$^{171}$Yb and $^{171}$Yb($^3$He,$\alpha\gamma$)$^{170}$Yb reactions. New data on $^{171}$Yb are compared to a previous measurement for $^{171}$Yb from the $^{172}$Yb($^3$He,$\alpha\gamma$)$^{171}$Yb reaction. Systematics of level densities and radiative strength functions in $^{170,171,172}$Yb are established. The entropy excess in $^{171}$Yb relative to the even-even nuclei $^{170,172}$Yb due to the unpaired neutron quasiparticle is found to be approximately 2$k_B$. Results for the radiative strength function from the two reactions lead to consistent parameters characterizing the ``pygmy'' resonances. Pygmy resonances in the $^{170,172}$Yb populated by the ($^3$He,$\alpha$) reaction appear to be split into two components for both of which a complete set of resonance parameters are obtained.Comment: 8 pages, 7 figure

Open femoral hernia repair: one skin incision for all

<p>Abstract</p> <p>Background</p> <p>Femoral hernias are relatively uncommon, however they are the most common incarcerated abdominal hernia, with strangulation of a viscus carrying significant mortality. Classically three approaches are described to open femoral hernia repair: Lockwood's infra-inguinal, Lotheissen's trans-inguinal and McEvedy's high approach. Each approach describes a separate skin incision and dissection to access the femoral sac. The decision as to which approach to adopt, predominantly dependent on the suspicion of finding strangulated bowel, is often a difficult one and in our opinion an unnecessary one.</p> <p>Methods</p> <p>We propose a technique for open femoral hernia repair that involves a single skin incision 1 cm above the medial half of the inguinal ligament that allows all of the above approaches to the hernia sac depending on the operative findings. Thus the repair of simple femoral hernias can be performed from below the inguinal ligament. If found, inguinal hernias can be repaired. More importantly, resection of compromised bowel can be achieved by accessing the peritoneal cavity with division of the linea semilunaris 4 cm above the inguinal ligament. This avoids compromise of the inguinal canal, and with medial retraction of the rectus abdominis muscle enables access to the peritoneal cavity and compromised bowel.</p> <p>Discussion</p> <p>This simple technique minimises the preoperative debate as to which incision will allow the best approach to the femoral hernia sac, allow for alteration to a simple inguinal hernia repair if necessary, and more importantly obviate the need for further skin incisions if compromised bowel is encountered that requires resection.</p