Yield stress fluids and fundamental particle statistics

Yield stress in complex fluids is described by resorting to fundamental statistical mechanics for clusters with different particle occupancy numbers. Probability distribution functions are determined for canonical ensembles of volumes displaced at the incipient motion in three representative states (single, double, and multiple occupancies). The statistical average points out an effective solid fraction by which the yield stress behavior is satisfactorily described in a number of aqueous (Si3N4, Ca3(PO4)2, ZrO2, and TiO2) and non-aqueous (Al2O3/decalin and MWCNT/PC) disperse systems. Interestingly, the only two model coefficients (maximum packing fraction and stiffness parameter) turn out to be correlated with the relevant suspension quantities. The latter relates linearly with (Young’s and bulk) mechanical moduli, whereas the former, once represented versus the Hamaker constant of two particles in a medium, returns a good linear extrapolation of the packing fraction for the simple cubic cell, here recovered within a relative error ≈ 1.3%

Tof ion spectra de convolution for lasergenerated plasmas

EnA study of different targets (Fe, Ti, Ni, Al2O3) ablation, in vacuum, by using a ns Nd:YAG laser radiation, 1064 nm and 532 nm (second harmonic) wavelengths, is reported. Laser pulse with high intensity generates a plasma at the target surface, with high non-isotropic emission of neutral and ion species, mainly emitted along the normal to the target surface. Time of flight (TOF) measurements are performed by using an ion collector consisting of a collimated Faraday cup placed along the normal to the target surface and an Ion Energy Analyzer (IEA) detector. The TOF spectra are converted as a function of the ions velocity and they are deconvolved for the various ion charge states by using the “Coulomb-Boltzmann shifted” function approach through the “Peakfit” mathematical code. The fit of the experimental distribution data permits to estimate the equivalent plasma temperature and the average energy shift of the distributions as a function of the ion charge state. This energy shift leads to the evaluation of the electric field producing the ion acceleration inside the plasma

Comparative cytogenetics on eight Malagasy Mantellinae (Anura, Mantellidae) and a synthesis of the karyological data on the subfamily

We performed a molecular and cytogenetic analysis on different Mantellinae species and revised the available chromosomal data on this group to provide an updated assessment of its karyological diver sity and evolution. Using a fragment of the mitochondrial 16S rRNA, we performed a molecular taxo nomic identification of the samples that were used for cytogenetic analyses. A comparative cytogenetic analysis, with Giemsa’s staining, Ag-NOR staining and sequential C-banding + Giemsa + CMA + DAPI was performed on eight species: Gephyromantis sp. Ca19, G. striatus (Vences, Glaw, Andreone, Jesu et Schimmenti, 2002), Mantidactylus (Chonomantis) sp. Ca11, M. (Brygoomantis) alutus (Peracca, 1893), M. (Hylobatrachus) cowanii (Boulenger, 1882), Spinomantis prope aglavei “North” (Methuen et Hewitt, 1913), S. phantasticus (Glaw et Vences, 1997) and S. sp. Ca3. Gephyromantis striatus, M. (Brygoomantis) alutus and Spinomantis prope aglavei “North” have a karyotype of 2n = 24 chromosomes while the other species show 2n = 26 chromosomes. Among the analysed species we detected differences in the number and position of telocentric elements, location of NOR loci (alternatively on the 6th, 7th or 10th pair) and in the distribution of heterochromatin, which shows species-specific patterns. Merging our data with those previously available, we propose a karyotype of 2n = 26 with all biarmed elements and loci of NORs on the 6th chromosome pair as the ancestral state in the whole family Mantellidae. From this putative ancestral condition, a reduction of chromosome number through similar tandem fusions (from 2n = 26 to 2n = 24) occurred independently in Mantidactylus Boulenger, 1895 (subgenus Brygoomantis Dubois, 1992), Spinomantis Dubois, 1992 and Gephyromantis Methuen, 1920. Similarly, a relocation of NORs, from the putative primitive configuration on the 6th chromosome, occurred independently in Gephyroman tis, Blommersia Dubois, 1992, Guibemantis Dubois, 1992, Mantella Boulenger, 1882 and Spinomantis. Chromosome inversions of primitive biarmed elements likely generated a variable number of telocentric elements in Mantella nigricans Guibé, 1978 and a different number of taxa of Gephyromantis (subgenera Duboimantis Glaw et Vences, 2006 and Laurentomantis Dubois, 1980) and Mantidactylus (subgenera Brygoomantis, Chonomantis Glaw et Vences, 1994, Hylobatrachus Laurent, 1943 and Ochthomantis Glaw et Vences, 1994)

Karyological diversification in the genus lyciasalamandra (Urodela: Salamandridae)

We performed the first cytogenetic analysis on five out of the seven species of the genus Lyciasalamandra, including seven subspecies, and representatives of its sister genus Salamandra. All the studied species have a similar karyotype of 2n = 24, mostly composed of biarmed elements. C-bands were observed on all chromosomes, at centromeric, telomeric and interstitial position. We found a peculiar taxon-specific NOR configuration, including either heteromorphic and homomorphic NORs on distinct regions of different chromosomes. Lyciasalamandra a. antalyana and L. helverseni showed two homomorphic NORs (pairs 8 and 2, respectively), while heteromorphic NORs were found in L. billae (pairs 6, 12), L. flavimembris (pairs 2, 12), L. l. luschani (pairs 2, 12), L. l. basoglui (pairs 6, 12), L. l. finikensis (pairs 2, 6) and S. lanzai (pairs 8, 10). Homomorphic NORs with an additional supernumerary site were shown by S. s. salamandra (pairs 2, 8) and S. s. gigliolii (pairs 2, 10). This unexpected highly variable NOR configuration is probably derived from multiple independent NOR translocations and paracentric inversions and correlated to lineage divergence in Lyciasalamandra. These results support the taxonomic validity of the studied taxa and are consistent with a hypothesized scenario of synchronous evolution in the genus

Statistical thermodynamics in reversible clustering of gold nanoparticles. A first step towards nanocluster heat engines

A statistical thermodynamics variational criterion is propounded to study thermal hysteresis in reversible clustering of gold (Au) nanoparticles. Experimentally, a transient equilibrium mapping analysis is employed to characterize it thermodynamically, further measurements being performed at the nanostructural and electrochemical levels (UV-Vis-NIR spectra, SLS/SAXS, zeta potential). Theoretically, it is successfully interpreted as a thermodynamic cycle, prompting that nanoclusters has potential to produce useful work from heat and paving the way to nanoclustering heat engines. By taking into account the virial expansion of hysteretic pressure, an entropy measure is deduced for a dilute system with given virial coefficients. This allows us to figure out the role of relevant interparticle potential parameters (i.e. surface potential, nanoparticle size, Debye's length, Hamaker energy) in both isothermal and isochoric variations at the onset of hysteresis. Application to spherical Au nanoparticles in watery salt solution (NaCl) is developed when an ad-hoc (DLVO) pairwise potential governs the second virial coefficient at the nanoscale. In particular, the variational criterion predicts a pressure drop between heating and cooling paths which is likely at the base of some energy redistribution (e.g. ordering/restructuring of electric double layers). We found an integrating factor that is able to numerically predict the existence of a critical value for the initial salt concentration maximizing the hysteretic area, and the effect of nanoparticle size on the cycle extent.A.A. and A.I acknowledge the Grant PID2021-123438NB-I00 funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe”, as well as financial support of Eusko Jaurlaritza, code: IT-1566-22 and from the IKUR Strategy. A. I. thanks MICINN for a Personal Técnico de Apoyo contract (PTA2017-14359-I). Correspondence of one of the authors (S.A.M.) with Dezső Boda (IASK/UP - Hungary) is kindly acknowledged. This work was supported by grant PID2019-111772RB-I00 funded by MCIN/AEI/ 10.13039/501100011033

Chromosome diversity and evolution in helicoide a (Gastropoda: Stylommatophora): A synthesis from original and literature data

We performed a molecular and a comparative cytogenetic analysis on different Helicoidea species and a review of all the available chromosome data on the superfamily to provide an updated assessment of its karyological diversity. Standard karyotyping, banding techniques, and Fluorescence in situ hybridization of Nucleolus Organizer Region loci (NOR-FISH) were performed on fifteen species of three families: two Geomitridae, four Hygromiidae and nine Helicidae. The karyotypes of the studied species varied from 2n = 44 to 2n = 60, highlighting a high karyological diversity. NORs were on a single chromosome pair in Cernuella virgata and on multiple pairs in four Helicidae, representing ancestral and derived conditions, respectively. Heterochromatic C-bands were found on pericentromeric regions of few chromosomes, being Q-and 4′,6-diamidino-2-phenylindole (DAPI) negative. NOR-associated heterochromatin was C-banding and chromomycin A3 (CMA3) positive. Considering the available karyological evidence on Helicoidea and superimposing the chromosome data gathered from different sources on available phylogenetic inferences, we describe a karyotype of 2n = 60 with all biarmed elements as the ancestral state in the superfamily. From this condition, an accumulation of chromosome translocations led to karyotypes with a lower chromosome number (2n = 50–44). This process occurred independently in different lineages, while an augment of the chromosome number was detectable in Polygyridae. Chromosome inversions were also relevant chromosome rearrangements in Helicoidea, leading to the formation of telocentric elements in karyotypes with a relatively low chromosome count