Two-step Melting Research Articles

Melting of dust plasma crystals with defects

The role of defects in the melting transition of a bilayer dust plasma crystal with vertical alignment is studied using Langevin molecular dynamics simulations. Two types of defects are considered: (i) point defects and dislocations and (ii) additional particles which are placed below and above the bilayer crystal (i.e., the so-called strong defects). It is shown that the presence of point defects and a few dislocations does not change the two-step melting scenario previously found for nondefect bilayer crystals. This contrast with the influence of the strong defects which leads to a substantial increase of the kinetic energy of particles and to local heating of the bilayer dust crystal.

Influence of the softness of the repulsive core interaction on cluster melting

The influence of the softness of the repulsive core of the pair interaction on the melting behavior of small clusters was studied by molecular-dynamics simulation of clusters in which particles interact through pairwise additive, inverse-power-based potentials. The potentials used had minima of the same depth and position and were identical beyond the minimum, differing only in the softness of the repulsive core. Core softness was found to favor a two-step cluster melting process.

2019 Immediate early gene C/EBP expression during long term memory in Aplysia

New passive and active oxysulfide glasses have been prepared in the Ge–Ga–Sb–S–O system employing a two-step melting process which involves the processing of the chalcogenide glass (ChG) and its subsequent melting with amorphous GeO2 or Sb2O3 powder. Optical characterization of the oxysulfide glasses has shown that the UV cut-off wavelength decreases with increasing oxygen content. Using Raman spectroscopy, correlations have been made between the formation of new Ge- and Sb-based oxysulfide structural units, the Sb content and the O/S ratio. We demonstrate the successful processing of active rare earth doped oxysulfide glasses by melting the chalcogenide glass with Er2O3 and Sb2O3 and also by melting the Er3+ doped chalcogenide glass with Sb2O3. Modification of the emission spectra at 1500 nm of Er3+ doped samples with the introduction of oxygen revealed that Er3+ most likely exists in dual O- and S-neighbor environments. Finally, the photo-response of these new glasses upon near-IR femtosecond laser irradiation has been investigated as a function of Sb content and O/S ratio and shows that the glasses are photo-sensitive to NIR fs laser light with the magnitude of the photo-sensitivity dependent on the glass’ Sb content and O/S ratio.

2020 Antinociceptive effect of p-hydroxymercuribenzoate through the spinal dynorphin system

New passive and active oxysulfide glasses have been prepared in the Ge–Ga–Sb–S–O system employing a two-step melting process which involves the processing of the chalcogenide glass (ChG) and its subsequent melting with amorphous GeO2 or Sb2O3 powder. Optical characterization of the oxysulfide glasses has shown that the UV cut-off wavelength decreases with increasing oxygen content. Using Raman spectroscopy, correlations have been made between the formation of new Ge- and Sb-based oxysulfide structural units, the Sb content and the O/S ratio. We demonstrate the successful processing of active rare earth doped oxysulfide glasses by melting the chalcogenide glass with Er2O3 and Sb2O3 and also by melting the Er3+ doped chalcogenide glass with Sb2O3. Modification of the emission spectra at 1500 nm of Er3+ doped samples with the introduction of oxygen revealed that Er3+ most likely exists in dual O- and S-neighbor environments. Finally, the photo-response of these new glasses upon near-IR femtosecond laser irradiation has been investigated as a function of Sb content and O/S ratio and shows that the glasses are photo-sensitive to NIR fs laser light with the magnitude of the photo-sensitivity dependent on the glass’ Sb content and O/S ratio.

Antinociceptive effect of -Hydroxymercuribenzoate through the spinal dynorphin system

New passive and active oxysulfide glasses have been prepared in the Ge–Ga–Sb–S–O system employing a two-step melting process which involves the processing of the chalcogenide glass (ChG) and its subsequent melting with amorphous GeO2 or Sb2O3 powder. Optical characterization of the oxysulfide glasses has shown that the UV cut-off wavelength decreases with increasing oxygen content. Using Raman spectroscopy, correlations have been made between the formation of new Ge- and Sb-based oxysulfide structural units, the Sb content and the O/S ratio. We demonstrate the successful processing of active rare earth doped oxysulfide glasses by melting the chalcogenide glass with Er2O3 and Sb2O3 and also by melting the Er3+ doped chalcogenide glass with Sb2O3. Modification of the emission spectra at 1500 nm of Er3+ doped samples with the introduction of oxygen revealed that Er3+ most likely exists in dual O- and S-neighbor environments. Finally, the photo-response of these new glasses upon near-IR femtosecond laser irradiation has been investigated as a function of Sb content and O/S ratio and shows that the glasses are photo-sensitive to NIR fs laser light with the magnitude of the photo-sensitivity dependent on the glass’ Sb content and O/S ratio.

Two-step melting of 2-propanol adsorbed on graphite

The x-ray diffraction measurements of 2-propanol adsorbed on graphite have been taken over the temperature range 150–240 K and the coverage range 2.28–4.23 molecules/nm2. The analysis of the data by means of the least-squares fitting of the complete pattern suggests that 2-propanol dimers bound by hydrogen bonding are arranged to give a lamellar structure of the molecules on the surface. The melting of the solid monolayers occurs by a two-step process involving an intermediate phase, possibly a defective two-dimensional smectic liquid crystal. The results are compared with the melting behavior observed for the monolayers of n-propanol.

Free-expansion melting of two dimensional colloidal crystals

Abstract Two-dimensional (2D) melting transitions have been observed in two freely expanding colloidal monolayer crystals formed from 1.01 μm polystyrene microspheres in an aqueous suspension between parallel optical flats, and with expansion rates differing by a factor of six. The data consist of digitized images of the 2D microsphere populations within a fixed sample area made from video records of the entire transition from ordered solid to liquid. The correlation functions computed from these data are consistent with a continuous two-step melting transition. However, direct observations of the time development of defect creation and evolution reveal that the systems may melt via a first order process. Although the melting rates differed appreciably, the results of the two melts are essentially the same.

Monte Carlo study of two-step defect melting

We present a detailed Monte Carlo study of the recently proposed model of defect melting in two dimensions exhibiting a crossover from a single first-order melting transition to two successive transitions of the Kosterlitz-Thouless type. The distinguishing parameter of this model is the length scale l of rotational stiffness.

Free-expansion melting of a colloidal monolayer.

A two-dimensional melting transition has been observed in a freely expanding colloidal monolayer lattice formed of 1.01-\ensuremath{\mu}m polystyrene microspheres in an aqueous suspension between two parallel optical flats. The correlation functions computed from digitized images of the particle distribution within a fixed sampling area are consistent with a continuous two-step melting transition. However, direct observations of defect creation and evolution reveal that the system may melt via a first-order process.

Thermally induced order-disorder transitions in Langmuir-Blodgett films

Structural studies of Langmuir-Blodgett (LB) monolayers at elevated temperatures reveal the onset of structural disorder. A two-step melting process in LB monolayer assemblies of cadmium arachidate has been observed by transmission and grazing incidence reflection IR spectroscopy in conjunction with Raman spectroscopy and thermal measurements. Prior to the melting point, a pretransitional disordering of the hydrocarbon tails was observed, followed by a catastrophic break-up of the cadmium lattice at a temperature corresponding to the melting point as measured by differential scanning calorimetry. This thermal behavior has been modified by the incorporation of aromaticity into the molecular head group. Our IR studies of the thermal behavior of the cadmium salts of tetradecyl benzoic acid and 2-nitro-5( N-methyl, N-octadecyl) amino benzoic acid as LB films indicate that the introduction of aromaticity into the head group improves the high temperature stability of the films. We attribute this behavior to the enhanced intermolecular interactions between the head groups.

Phase Relation ofp-n-Hexyloxybenzylidene-p'-toluidine (HBT) as Revealed by Thermal and Microscopic Studies

Abstract Complex phase relation of a mesogen compound, HBT, was established by extensive DTA and microscopic texture observations. The two-step melting behavior reported previously was due to the coexistence of the two crystalline phases, Crystal I and Crystal II, which have different melting points to the nematic phase because the rate of transition between them is very slow. The conditions have been revealed under which each of the pure crystalline phases may be realized. Coexistence of the crystalline and the nematic phases is confirmed visually under a polarizing microscope at temperatures between the two melting points.

Observation of a Two-Step Melting in the Submonolayer Region of Tetramethyltin Sn(CH3)4Adsorbed on (0001) Graphite, by Mössbauer Spectroscopy

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Observation of a Two-Step Melting in the Submonolayer Region of Tetramethyltin Sn(CH_{3})_{4} Adsorbed on (0001) Graphite, by Mössbauer Spectroscopy

Observation of a Two-Step Melting in the Submonolayer Region of Tetramethyltin Sn(CH_{3})_{4} Adsorbed on (0001) Graphite, by Mössbauer Spectroscopy

Distribution of histone F1 on calf thymus nucleohistone DNA

A method of large-scale preparation of the histone F1-DNA complex by removing all other proteins from calf thymus nucleohistone was established. This involved gel filtration of nucleohistone through a column containing a band of sodium dodecyl sulfate. The F1-DNA complex obtained had the original amount of F1 and no other. The F1-DNA complex exhibited distinct two-step melting on thermal denaturation. The first step was apparently attributable to naked DNA regions and the second step, about 30 deg. C higher than the first step, to the regions covered with F1. Buoyant density experiments with the complex after fixation with formalin revealed that F1 was distributed fairly evenly over DNA fragments of an average molecular weight of about 4 × 10 6. Electron microscopic examination of the complex after various degrees of denaturation with formalin indicated that the longest stretch of unbound DNA was about 0·3 μm.

Properties of chromosomal nucleohistone

The deoxyribonucleohistone component may be physically separated from the other components of pea embryo chromatin. Such nucleohistone differs from deproteinized pea embryo DNA in its higher melting temperature, in its histone/DNA mass ratio (1·3: I) and in its inactivity in the support of DNA-dependent RNA synthesis. Pea embryo chromatin contains DNA not only as nucleohistone but also as DNA not so complexed. This is indicated by the two-step melting profile of chromatin as well as by the ability of chromatin to support DNA-dependent RNA synthesis. Approximately 80% of the DNA of pea embryo chromatin is bound in the form of nucleohistone; the remaining 20% appears to be present as DNA not complexed with histone.