Glass transition and layering effects in confined water: a computer simulation study

Single particle dynamics of water confined in a nanopore is studied through Computer Molecular Dynamics. The pore is modeled to represent the average properties of a pore of Vycor glass. Dynamics is analyzed at different hydration levels and upon supercooling. At all hydration levels and all temperatures investigated a layering effect is observed due to the strong hydrophilicity of the substrate. The time density correlators show, already at ambient temperature, strong deviations from the Debye and the stretched exponential behavior. Both on decreasing hydration level and upon supercooling we find features that can be related to the cage effect typical of a supercooled liquid undergoing a kinetic glass transition. Nonetheless the behavior predicted by Mode Coupling Theory can be observed only by carrying out a proper shell analysis of the density correlators. Water molecules within the first two layers from the substrate are in a glassy state already at ambient temperature (bound water). The remaining subset of molecules (free water) undergoes a kinetic glass transition; the relaxation of the density correlators agree with the main predictions of the theory. From our data we can predict the temperature of structural arrest of free water.Comment: 14 pages, 15 figures inserted in the text, to be published in J. Chem. Phys. (2000

Modifications of the hydrogen bond network of liquid water in a cylindrical SiO_2 pore

We present results of molecular dynamics simulations of water confined in a silica pore. A cylindrical cavity is created inside a vitreous silica cell with geometry and size similar to the pores of real Vycor glass. The simulations are performed at different hydration levels. At all hydration levels water adsorbs strongly on the Vycor surface; a double layer structure is evident at higher hydrations. At almost full hydration the modifications of the confinement-induced site-site pair distribution functions are in qualitative agreement with neutron diffraction experiment. A decrease in the number of hydrogen bonds between water molecules is observed along the pore radius, due to the tendency of the molecules close to the substrate to form hydrogen-bonds with the hydrophilic pore surface. As a consequence we observe a substrate induced distortion of the H-bond tetrahedral network of water molecules in the regions close to the surface.Comment: Talk presented at "Physics of Liquids: Foundations, Highlights, Challenge", Murau Sept. 1998. To appear in J. Mol. Li

Supercooled confined water and the Mode Coupling crossover temperature

We present a Molecular Dynamics study of the single particle dynamics of supercooled water confined in a silica pore. Two dynamical regimes are found: close to the hydrophilic substrate molecules are below the Mode Coupling crossover temperature, $T_C$, already at ambient temperature. The water closer to the center of the pore (free water) approaches upon supercooling $T_C$ as predicted by Mode Coupling Theories. For free water the crossover temperature and crossover exponent $\gamma$ are extracted from power-law fits to both the diffusion coefficient and the relaxation time of the late $\alpha$ region.Comment: To be published, Phys. Rev. Lett., 4 pages, 3 figures, revTeX, minor changes in the figures, references added, changes in the tex

Manufacture, observation, and test of membranes with locatable single pores

A method for generating single pores down to 0.1 μm diameter in the center of a large circular foil is described, based on nuclear tracks. The foil is framed by a tension ring which enables one to handle the foils in a well‐defined precise way. The single pore has a lateral displacement of ±0.1 mm with respect to the tension ring center. The foils used are polycarbonate of the type Makrofol and have thicknesses between 2 and 10 μm. For calibration of the single pore diameters, multiple nuclear tracks between 0.1 and 3.5 μm diameter are etched and observed by microscopy. The microscopic observations are compared with gas‐flow measurements, using two alternative methods: multiple holes are tested under viscous flow conditions of N2 gas at normal temperature and pressure; single holes are tested under collisionless flow conditions of 4He gas at liquid‐nitrogen temperature, using a capacitance method.Peer reviewe

Prevalência e fatores de risco associados à Leptospira spp. em rebanhos bovinos da região centro-sul do estado do Paraná.

O objetivo deste trabalho foi determinar a prevalência de anticorpos anti-Leptospira spp. e os fatores de risco para infecção de Leptospira spp. na criação de rebanhos bovinos no centro-sul da região do Estado do Paraná

X-ray Absorption Near-Edge Structure (XANES) at the O K-Edge of Bulk Co₃O₄: Experimental and Theoretical Studies

We combine theoretical and experimental X-ray absorption near-edge spectroscopy (XANES) to probe the local environment around cationic sites of bulk spinel cobalt tetraoxide (Co3O4). Specifically, we analyse the oxygen K-edge spectrum. We find an excellent agreement between our calculated spectra based on the density functional theory and the projector augmented wave method, previous calculations as well as with the experiment. The oxygen K-edge spectrum shows a strong pre-edge peak which can be ascribed to dipole transitions from O 1s to O 2p states hybridized with the unoccu- pied 3d states of cobalt atoms. Also, since Co3O4 contains two types of Co atoms, i.e., Co3+ and Co2+, we find that contribution of Co2+ ions to the pre-edge peak is solely due to single spin-polarized t2g orbitals (dxz, dyz, and dxy) while that of Co3+ ions is due to spin-up and spin-down polarized eg orbitals (dx2−y2 and dz2 ). Furthermore, we deduce the magnetic moments on the Co3+ and Co2+ to be zero and 3.00 μB respectively. This is consistent with an earlier experimental study which found that the magnetic structure of Co3O4 consists of antiferromagnetically ordered Co2+ spins, each of which is surrounded by four nearest neighbours of oppositely directed spins

The Interface of Cancer, Their Microenvironment and Nanotechnology

Cancer is one of the deadliest diseases with a cure far from being found. Despite the extraordinary advances in the therapy approaches, only a few patients respond to treatments. The tumor microenvironment (TME) plays a crucial role in cancer progression by contributing to the chemoresistance. Thus, emerging efforts are being made in nanotechnology research focusing on nanoparticles' potential role and their application in immune system modulation. Moreover, the omics have contributed to bioengineering and nanotechnology development by elucidating the mechanisms of cancer and specific biomarkers that could be used as new therapeutic targets. Furthermore, the non-coding microRNA as a target for cancer treatment and creation of organoids for the study of new treatments helped for the new therapeutics' era called personalized medicine. Here we will discuss the role played by TME in tumor initiation and progression we will describe the recent nanotechnology applied to cancer treatment. Specifically, we will describe the potential role of nanoparticles (NPs) and their application in immune system modulation, ultimately leading to circumventing tumor cell proliferation.publishersversionpublishe

Exploring the performance of the spectrometer prisma in heavy zirconium and xenon mass regions

We present results from two recent runs which illustrate the performance of the PRISMA spectrometer in the proximity of the upper limit of its operational interval, namely 96Zr + 124Sn at Elab = 500 MeV and 136Xe + 208Pb at Elab = 930 MeV. In the latter run, the γ array CLARA also allowed us to identify previously unknown γ transitions in the nuclides 136Cs and 134I

Prevalence of antibodies against Chlamydophila spp. in herds with bovine abortion of Paraná state, Brazil

Chlamydophila abortus é o agente etiológico do aborto epizoótico bovino, cujas manifestações clínicas mais freqüentes são aborto, nascimento de bezerros prematuros e de animais fracos, natimorto e repetição de cio em intervalos irregulares. O objetivo deste trabalho foi estimar a prevalência de anticorpos anti-Chlamydophila spp. em fêmeas bovinas de propriedades rurais com histórico de aborto, selecionadas dentro do delineamento amostral do Plano Nacional de Controle e Erradicação da Brucelose e Tuberculose no estado do Paraná. Foram testadas pela prova de fixação de complemento 3.102 amostras de soro de fêmeas bovinas (idade > 24 meses), provenientes de 373 propriedades. Ao total, 44 (1,42%) animais foram positivos com títulos > 32. A prevalência de focos foi de 8,82% (6,15%-12,17%). Animais confinados ou semi-confinados (OR=3.339, P=0.004), propriedade com menos de 35 matrizes (OR=3.339, P=0.017), presença de produtos do aborto na pastagem (OR=2.372, P=0.037) e aluguel de pasto (OR=3.398, P=0.006) foram considerados fatores de risco para Chlamydophila spp. A infecção por Chlamydophila spp. acometeu um número pequeno de animais, oriundos de propriedades com histórico de aborto. A importância deste agente como causa de aborto em bovinos no estado do Paraná, se existir, é muito pequena.Chlamydophila abortus is a recognized cause of bovine epizootic abortion. Abortion, premature birth and weak lamb/calf, stillbirth and repeat breeding in irregular intervals are the most frequent disease manifestations. The complement fixation test is the recommended by the World Organization of Animal Health (OIE) for Chlamydophila spp. serologic diagnosis. The aim of this study was estimate the prevalence of antibodies against Chlamydophila spp. in cattle herds with abortion, selected inside the sampling design of National Program of Control and Erradication of Brucellosis in Paraná state. Serum samples of 3,102 cows (age > 24 months) from 373 herds were analyzed by complement fixation test. Totally, 44 (1.42%) animal were positive with titers > 32. The seroprevalence of Chlamydophila spp. in the herds was 8.82% (6.15%-12.17%). Four variables were associated with seroprevalence for Chlamydophila spp. in the final model of logistic regression: confined or semi-confined breeding (OR=3.339, P=0.004), farms with less than 35 cows (OR=3.339, P=0.017), abortion in the pasture (OR=2.372, P=0.037) and pasture rent (OR=3.398, P=0.006) were risk factors for Chlamydophila spp. This bacterium infected a small number of cattle from herds with abortion in Paraná state. Chlamydophila spp impact as abortion cause is reduced in this state

MicroRNA profile changes in human immunodeficiency virus type 1 (HIV-1) seropositive individuals

MicroRNAs (miRNAs) play diverse roles in regulating cellular and developmental functions. We have profiled the miRNA expression in peripheral blood mononuclear cells from 36 HIV-1 seropositive individuals and 12 normal controls. The HIV-1-positive individuals were categorized operationally into four classes based on their CD4+ T-cell counts and their viral loads. We report that specific miRNA signatures can be observed for each of the four classes