Soft X-ray induced radiation damage in thin freeze-dried brain samples studied by FTIR microscopy

In order to push the spatial resolution limits to the nanoscale, synchrotron-based soft X-ray microscopy (XRM) experiments require higher radiation doses to be delivered to materials. Nevertheless, the associated radiation damage impacts on the integrity of delicate biological samples. Herein, the extent of soft X-ray radiation damage in popular thin freeze-dried brain tissue samples mounted onto Si3N4 membranes, as highlighted by Fourier transform infrared microscopy (FTIR), is reported. The freeze-dried tissue samples were found to be affected by general degradation of the vibrational architecture, though these effects were weaker than those observed in paraffin-embedded and hydrated systems reported in the literature. In addition, weak, reversible and specific features of the tissue–Si3N4 interaction could be identified for the first time upon routine soft X-ray exposures, further highlighting the complex interplay between the biological sample, its preparation protocol and X-ray probe

Evidence for a Soft Nuclear Equation-of-State from Kaon Production in Heavy Ion Collisions

The production of pions and kaons has been measured in Au+Au collisions at beam energies from 0.6 to 1.5 AGeV with the Kaon Spectrometer at SIS/GSI. The K+ meson multiplicity per nucleon is enhanced in Au+Au collisions by factors up to 6 relative to C+C reactions whereas the corresponding pion ratio is reduced. The ratio of the K+ meson excitation functions for Au+Au and C+C collisions increases with decreasing beam energy. This behavior is expected for a soft nuclear equation-of-state.Comment: 14 pages, 2 figures, accepted for publication in Phys. Rev. Let

Production of Charged Pions, Kaons and Antikaons in Relativistic C+C and C+Au Collisions

Production cross sections of charged pions, kaons and antikaons have been measured in C+C and C+Au collisions at beam energies of 1.0 and 1.8 AGeV for different polar emission angles. The kaon and antikaon energy spectra can be described by Boltzmann distributions whereas the pion spectra exhibit an additional enhancement at low energies. The pion multiplicity per participating nucleon M(pi+)/A_part is a factor of about 3 smaller in C+Au than in C+C collisions at 1.0 AGeV whereas it differs only little for the C and the Au target at a beam energy of 1.8 AGeV. The K+ multiplicities per participating nucleon M(K+)/A_part are independent of the target size at 1 AGeV and at 1.8 AGeV. The K- multiplicity per participating nucleon M(K-)/A_part is reduced by a factor of about 2 in C+Au as compared to C+C collisions at 1.8 AGeV. This effect might be caused by the absorption of antikaons in the heavy target nucleus. Transport model calculations underestimate the K-/K+ ratio for C+C collisions at 1.8 AGeV by a factor of about 4 if in-medium modifications of K mesons are neglected.Comment: 19 pages, 14 figures, accepted for publication in Eur. Phys. J.

Low-energy cross section of the 7Be(p,g)8B solar fusion reaction from Coulomb dissociation of 8B

Final results from an exclusive measurement of the Coulomb breakup of 8B into 7Be+p at 254 A MeV are reported. Energy-differential Coulomb-breakup cross sections are analyzed using a potential model of 8B and first-order perturbation theory. The deduced astrophysical S_17 factors are in good agreement with the most recent direct 7Be(p,gamma)8B measurements and follow closely the energy dependence predicted by the cluster-model description of 8B by Descouvemont. We extract a zero-energy S_17 factor of 20.6 +- 0.8 (stat) +- 1.2 (syst) eV b.Comment: 14 pages including 16 figures, LaTeX, accepted for publication in Physical Review C. Minor changes in text and layou

Medium Effects in Kaon and Antikaon Production in Nuclear Collisions at Subthreshold Beam Energies

Production cross sections of K$^+$ and K$^-$ mesons have been measured in C+C collisions at beam energies per nucleon below and near the nucleon-nucleon threshold. At a given beam energy, the spectral slopes of the K$^-$ mesons are significantly steeper than the ones of the K$^+$ mesons. The excitation functions for K$^+$ and K$^-$ mesons nearly coincide when correcting for the threshold energy. In contrast, the K$^+$ yield exceeds the K$^-$ yield by a factor of about 100 in proton-proton collisions at beam energies near the respective nucleon-nucleon thresholds.Comment: Accepted for publication in Phys. Rev. Let

Three-point function of semiclassical states at weak coupling

We give the derivation of the previously announced analytic expression for the correlation function of three heavy non-BPS operators in N=4 super-Yang-Mills theory at weak coupling. The three operators belong to three different su(2) sectors and are dual to three classical strings moving on the sphere. Our computation is based on the reformulation of the problem in terms of the Bethe Ansatz for periodic XXX spin-1/2 chains. In these terms the three operators are described by long-wave-length excitations over the ferromagnetic vacuum, for which the number of the overturned spins is a finite fraction of the length of the chain, and the classical limit is known as the Sutherland limit. Technically our main result is a factorized operator expression for the scalar product of two Bethe states. The derivation is based on a fermionic representation of Slavnov's determinant formula, and a subsequent bosonisation.Comment: 28 pages, 5 figures, cosmetic changes and more typos corrected in v

Effetti dell’inquinamento da plastiche sui foraminiferi bentonici

Le plastiche sono divenuti contaminanti ubiquitari negli ecosistemi marini, d’acqua dolce e terrestri che producono rilevanti impatti sulle specie che in essi vivono. Dal 1950 ad oggi sono stati accumulati nell’ambiente circa 5 miliardi di tonnellate di plastica (Geyer et al., 2017). I meccanismi di interazione tra microplastiche e biosfera nonché gli effetti biochimici delle molecole sintetiche, specialmente sugli organismi eucariotici unicellulari marini, sono scarsamente studiati. In particolare, i foraminiferi bentonici costituiscono una componente fondamentale delle comunità marine e svolgono un ruolo chiave nel funzionamento dell’ecosistema e nei cicli biogeochimici. La loro sensibilità e la rapida risposta allo stress ambientale li rendono efficienti indicatori dei cambiamenti climatici e ambientali attuali e del passato (Schönfeld et al., 2012).Per comprendere meglio l’effetto delle plastiche negli oceani e negli organismi marini, abbiamo valutato l’incorporazione di (bio)polimeri e microplastiche in foraminiferi bentonici utilizzando tecniche di spettromicroscopia ad infrarossi in trasformata di Fourier (μFTIR). In questo studio, abbiamo raccolto ed analizzato spettri ed immagini μFTIR dauna selezione di specie di foraminiferi bentonici: Rosalina globularis cresciuta in colture inquinate con la plastica e Cibicidoides lobatulus, Rosalina bradyi e Textularia bocki raccolti su un frammento di plastica trovato sepolto in un sedimento del fondale del Mar Mediterraneo. In particolare, i foraminiferi provenienti dalle colture sono stati intossicati con molecola di di-2-etilesilftalato (DEHP) allo scopo di valutarne l’incorporazione nel citoplasma. Questo studio ha permesso di documentare: (1) la presenza di microplastiche nel citoplasma e nel guscio agglutinante di T. bocki; (2) segnali di stress ossidativo e di aggregazione proteica nella componente cellulare di C. lobatulus, R. bradyi e T. bocki, ancorati alla busta di plastica; (3) l’incorporazione del DEHP nel citoplasma di R. globularis. Questo studio ha confermato il ruolo chiave svolto dai foraminiferi bentonici come proxy per la valutazione degli effetti dell’inquinamento da microplastiche sia a livello cellulare che di biomineralizzazione confermando l’ingresso delle microplastiche e DEHP nei cicli biogeochimici. Questa indagine ha inoltre dimostrato che la microscopia FTIR è uno strumento efficace per studiare, senza l’utilizzo di marcatori specifici, l’interazione su scala molecolare tra plastica, citoplasma e guscio dei foraminiferi