Observation of a correlated free four-neutron system

A long-standing question in nuclear physics is whether chargeless nuclear systems can exist. To our knowledge, only neutron stars represent near-pure neutron systems, where neutrons are squeezed together by the gravitational force to very high densities. The experimental search for isolated multi-neutron systems has been an ongoing quest for several decades1, with a particular focus on the four-neutron system called the tetraneutron, resulting in only a few indications of its existence so far2–4, leaving the tetraneutron an elusive nuclear system for six decades. Here we report on the observation of a resonance-like structure near threshold in the four-neutron system that is consistent with a quasi-bound tetraneutron state existing for a very short time. The measured energy and width of this state provide a key benchmark for our understanding of the nuclear force. The use of an experimental approach based on a knockout reaction at large momentum transfer with a radioactive high-energy 8 He beam was key.S

Analytical approach to electromagnetic processes in loosely bound nuclei: application to 8B

In this paper we develop an analytical model in order to study electromagnetic processes involving loosely bound neutron--rich and proton--rich nuclei. We construct a model wave function, to describe loosely bound few--body systems, having the correct behaviour both at large and small distances. The continuum states are approximated by regular Coulomb functions. As a test case we consider the two--body Coulomb dissociation of 8B and, the inverse, radiative capture reaction. The difference between using a pure two--body model and the results obtained when incorporating many--body effects, is investigated. We conclude that the interpretation of experimental data is highly model dependent and stress the importance of measuring few--body channels.Comment: Accepted for publication in Physics Letters B. Added a comparison with a potential model calculation in Fig.

The influence of light and culture media on the growth of the red seaweed Gracilaria gracilis (Rhodophyta, Gracilariales) under laboratory conditions

info:eu-repo/semantics/publishedVersio

Wave scattering from self-affine surfaces

Electromagnetic wave scattering from a perfectly reflecting self-affine surface is considered. Within the framework of the Kirchhoff approximation, we show that the scattering cross section can be exactly written as a function of the scattering angle via a centered symmetric Levy distribution for general roughness amplitude, Hurst exponent and wavelength of the incident wave. The amplitude of the specular peak, its width and its position are discussed as well as the power law decrease (with scattering angle) of the scattering cross section.Comment: RevTeX, 4 pages including 2 figures. Submitted Phys. Rev. Let

Simultaneous gain and phase profile determination on an interferometric BOTDA

24th International Conference on Optical Fibre Sensors, 96343Y, Curitiba, Brazil, September 28, 2015.Up to now, complex (phase and intensity) measurements in Brillouin Optical Time-Domain Analysis (BOTDA) systems required complex phase modulation methods and high-bandwidth (multi-GHz) detection. In this work, we propose a novel technique that is able to retrieve simultaneously both gain/loss and phase characteristics of the Brillouin interaction by just introducing a Sagnac Interferometer (SI) 011 a standard BOTDA sensing scheme. The technique is described analytically and demonstrated experimentally. With this technique, a reliability increase is produced since redundant measurements can be performed.European CommissionMinisterio de Economía y CompetitividadUniversidad de AlcaláComunidad de MadridGeneralitat Valencian

Fast computation of the Gauss hypergeometric function with all its parameters complex with application to the Poschl-Teller-Ginocchio potential wave functions

The fast computation of the Gauss hypergeometric function 2F1 with all its parameters complex is a difficult task. Although the 2F1 function verifies numerous analytical properties involving power series expansions whose implementation is apparently immediate, their use is thwarted by instabilities induced by cancellations between very large terms. Furthermore, small areas of the complex plane are inaccessible using only 2F1 power series formulas, thus rendering 2F1 evaluations impossible on a purely analytical basis. In order to solve these problems, a generalization of R.C. Forrey's transformation theory has been developed. The latter has been successful in treating the 2F1 function with real parameters. As in real case transformation theory, the large canceling terms occurring in 2F1 analytical formulas are rigorously dealt with, but by way of a new method, directly applicable to the complex plane. Taylor series expansions are employed to enter complex areas outside the domain of validity of power series analytical formulas. The proposed algorithm, however, becomes unstable in general when |a|,|b|,|c| are moderate or large. As a physical application, the calculation of the wave functions of the analytical Poschl-Teller-Ginocchio potential involving 2F1 evaluations is considered.Comment: 29 pages; accepted in Computer Physics Communication

Water reconditioning by high power ultrasound combined with residual chemical sanitizers to inactivate foodborne pathogens associated with fresh-cut products

The suitability of high power ultrasound (HPU, 20 kHz, 0.28 kW/l) combined with residual chemical sanitizers for water reconditioning was studied. A synergetic disinfection effect was observed when HPU was combined with peroxyacetic acid (PAA) or a commercial mix of organic acids and phenolic compounds (OA/PC). In recycled water (RW) with a chemical oxygen demand (COD) of 500 mg O2/l, PAA inactivated 2 log units of Escherichia coli O157:H7 at concentrations of 3.2, 6.4, 16 mg/l after 7 min, 2 min, 29 s, respectively. The OA/PC or HPU treatments alone needed 26 min treatments to achieve the same reduction. The addition of TiO2 (5 g/l) to HPU (sonocatalysis) did not improve E. coli O157:H7 inactivation. However, when HPU was combined with a residual concentration of PAA (3.2 mg/l), the total inactivation of E. coli O157:H7 and Salmonella (6 log unit reductions) occurred after 11 min, but for Listeria monocytogenes only 1.7 log reductions were detected after 20 min. When HPU was combined with OA/PC, a synergistic effect for the inactivation of E. coli O157:H7 was also observed, but this sanitizer significantly modified the physical-chemical quality characteristics of the RW. These results show that the residual PAA concentration that can be found in the wash water combined with HPU could result in an environmentally friendlier and toxicologically safer strategy for water reconditioning of the fresh-cut industry. The use of the sanitizer alone requires higher concentrations and/or longer contacts times. Even though the residual PAA in combination with HPU was adequate for water reconditioning, it is not appropriate for the process wash water because this wash water must be instantaneously disinfected.Ciencias de la Alimentació

On the concentration and size distribution of sub-micron aerosol in the Galápagos Islands

During the CHARLEX campaign in the Galápagos Islands, a Scanning Particle Mobility Sizer was deployed on San Cristobal Island in July-August 2011 to carry out size-resolved measurements of the concentration of submicron aerosols. To our knowledge these are the first measurements of aerosol concentrations in this unique environment. The particles with marine origin displayed a tri-modal number size distribution with peak diameters of 0.016 μm, 0.050 μm and 0.174 μm and a cloud-processed intermodal minimum at 0.093 μm. The mean total aerosol number concentration for the marine contribution was 470 ± 160 cm. A low particle concentration of 70 ± 50 cm for the nucleation size range was measured, but no evidence of new particle production in the atmospheric marine boundary layer (MBL) was observed. The concentration of the Aitken size mode was found to be related to aerosol entrainment from the free troposphere off the coast of Chile followed by transport within the MBL to the Galápagos Islands. Cloud processing may activate the particles in the Aitken size range, growing through 'in-cloud' sulphate production and increasing the particle concentration in the accumulation size range. The 0.093 μm cloud processed minima suggests that the critical supersaturation at which the particle is activated to a cloud droplet is in the 0.14-0.21% range. The daytime marine particle background concentration was influenced by human activity around the sampling site, as well as by new particle formation triggered by biogenic emissions from the vegetation cover of the island's semiarid lowlands. Effective CCN formation may play a role in the formation and properties of the stratus clouds, which permanently cover the top of the windward side of the islands and establish one of their characteristic climatic bands.Peer Reviewe

Synthesis and Antiproliferative Activity of Sulfa-Michael Adducts and Thiochromenes Derived from Carbohydrates

The Michael addition reactions of carbohydrate-derived nitroalkenes with ethyl thioglycolate and 2-mercaptobenzyl alcohol were studied. Reactions were conducted under mild, solvent-free conditions with DABCO as a catalyst, affording the corresponding adducts in good yields. Furthermore, compounds resulting from the addition with 2-mercaptobenzyl alcohol were used as starting materials for the synthesis of chiral 3-nitro-2H-thiochromenes. For some of the compounds synthesized herein, the antioxidant and antiproliferative activities against a panel of human solid tumor cell lines were assayed and compared with those of carbohydrate-nitroalkene substrates.Junta de Extremadura GR15022Unión Europea FP7-REGPOT-2012-CT2012-31637-IMBRAI