scholarly journals Melting dynamics of ice in the mesoscopic regime

2017 ◽  
Vol 114 (23) ◽  
pp. 5935-5940 ◽  
Author(s):  
Margherita Citroni ◽  
Samuele Fanetti ◽  
Naomi Falsini ◽  
Paolo Foggi ◽  
Roberto Bini
Keyword(s):  
Phase Transitions ◽  
Time Resolution ◽  
Time Window ◽  
Thermal Contact ◽  
Mie Scattering ◽  
The Other ◽  
Complete Melting ◽  
Experimental Works ◽  
Melting Dynamics ◽  
Subnanosecond Time

How does a crystal melt? How long does it take for melt nuclei to grow? The melting mechanisms have been addressed by several theoretical and experimental works, covering a subnanosecond time window with sample sizes of tens of nanometers and thus suitable to determine the onset of the process but unable to unveil the following dynamics. On the other hand, macroscopic observations of phase transitions, with millisecond or longer time resolution, account for processes occurring at surfaces and time limited by thermal contact with the environment. Here, we fill the gap between these two extremes, investigating the melting of ice in the entire mesoscopic regime. A bulk ice Ih or ice VI sample is homogeneously heated by a picosecond infrared pulse, which delivers all of the energy necessary for complete melting. The evolution of melt/ice interfaces thereafter is monitored by Mie scattering with nanosecond resolution, for all of the time needed for the sample to reequilibrate. The growth of the liquid domains, over distances of micrometers, takes hundreds of nanoseconds, a time orders of magnitude larger than expected from simple H-bond dynamics.

Hyperfine Structure in the Radio Spectra of Jupiter

1973 ◽  
Vol 2 (4) ◽  
pp. 191-193 ◽  
Author(s):  
G. R. A. Ellis
Keyword(s):  
Hyperfine Structure ◽  
Time Scales ◽  
Time Resolution ◽  
The Other ◽  
Radio Emissions ◽  
Other Hand ◽  
Different Time Scales

Observations of the Jupiter radio emissions have established that the radiation is normally received as bursts with two quite different time scales. The L bursts mostly have durations of 1-10 seconds, although extended bursts up to 100 seconds are sometimes observed. The S bursts on the other hand have time scales of milliseconds and fractions of a millisecond. Dynamic spectrographic observations have shown that both types are structured in the frequency-time plane although the frequency and time resolution used so far has been insufficient to investigate detail smaller than 50 KHz and 10 msec respectively.

Newborns Crying in Different Contexts: Discrete or Graded Signals?

1998 ◽  
Vol 86 (3_suppl) ◽  
pp. 1123-1140 ◽  
Author(s):  
D. Lenti Boero ◽  
C. Bianchi ◽  
C. Volpe ◽  
A. Marcello ◽  
C. Lenti
Keyword(s):  
Time Window ◽  
Interesting Property ◽  
The Other ◽  
Acoustic Features ◽  
Acoustic Parameters ◽  
Long Distance ◽  
Human Infants ◽  
Context Type ◽  
Normal Human ◽  
Individual Specificity

The aim of this study was to investigate whether human infants' cries show individually and contextually discriminable acoustic parameters. 20 full-term normal human newborns (aged 1 to 4 days) had their cries recorded during routine blood withdrawal (pain context) 30 min. before a scheduled feeding (hunger context) and when subjected to kinetic stimuli during neurological examination (manipulation context). Type of cries, melodic contours, F0 parameters, but not the “macro” trend of the start of the fundamental frequency, indicated a difference in pain cries in the other two contexts. All the acoustic features considered showed an individual specificity. The peak frequencies of voiceless or partially voiced wails had the interesting property of being optimised as long distance signals. We hypothesised that this feature of infants' cries may have evolved in a time window when the infants were left in collective nurseries and not carried on the mothers' backs as maintained by the traditional view.

Structure of [(CH3)2NH2]2CoCl4 at elevated temperatures

1999 ◽  
Vol 55 (5) ◽  
pp. 752-757 ◽  
Author(s):  
Amir H. Mahmoudkhani ◽  
Vratislav Langer
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonding ◽  
Phase Transitions ◽  
Physical Properties ◽  
Electric Conductivity ◽  
Title Compound ◽  
Structural Changes ◽  
Elevated Temperatures ◽  
The Other ◽  
Cell Parameters

The crystal structure of the title compound, dimethylammonium tetrachlorocobaltate(II), has been determined at four temperatures between 297 and 366 K, in order to investigate possible phase transitions at 313 and 353 K [Kapustianik, Polovinko & Kaluza et al. (1996). Phys. Status Solidi A, 153, 117–122]. We found that there is no significant change either in the hydrogen-bonding network or in the cell parameters, apart from a linear dilatation with temperature. This study reveals that the anomalous variation in electric conductivity and some of the other physical properties of the compound cannot be explained by structural changes.

An in situ study of the phase transitions among CaCO3 high-pressure polymorphs

2018 ◽  
Vol 83 (02) ◽  
pp. 191-197 ◽  
Author(s):  
Xueyin Yuan ◽  
Chao Gao ◽  
Jing Gao
Keyword(s):  
Phase Transitions ◽  
Intermediate Phase ◽  
The Other ◽  
Three Samples ◽  
Short Period ◽  
Two Samples ◽  
Wide Pressure Range ◽  
Diamond Anvil ◽  
Wide Pressure

AbstractThe phase transitions involving calcite (CaCO3-I), CaCO3-II, CaCO3-III and CaCO3-IIIb were investigated using a diamond anvil cell and micro-Raman spectroscopy. Based on the results obtained from in situ observations and Raman measurements made with six natural calcite crystals, the phase transition from calcite to CaCO3-II took place between 1.56 and 1.67 GPa under ambient temperature. Under a precise pressure of 1.97 ± 0.03 GPa, three CaCO3 samples were observed to transform from CaCO3-II directly to CaCO3-III, while in the other three samples both CaCO3-III and CaCO3-IIIb crystal structures were detected. Transformation from CaCO3-IIIb to CaCO3-III was completed in a short period in one sample, whereas in the other two samples coexistence of CaCO3-III and CaCO3-IIIb was observed over a wide pressure range from 1.97 to 3.38 GPa, with sluggish transformation from CaCO3-IIIb to CaCO3-III being observed after the samples were preserved under 3.38 GPa for 72 h. Hence, it can be concluded that CaCO3-IIIb is a metastable intermediate phase occurring during the reconstructive transformation from CaCO3-II to CaCO3-III. Splitting of the C–O in-plane bending (ν4) and symmetric stretching (ν1) vibrations and appearance of new lattice vibrations in the Raman spectra of CaCO3-III and CaCO3-IIIb suggest a lowering in crystal symmetry during the transformation from CaCO3-II through CaCO3-IIIb to CaCO3-III, which is in good agreement with the observed sequence of phase symmetries.

Superficial Phase Transitions in Nanoalloys

2011 ◽  
Vol 172-174 ◽  
pp. 658-663 ◽  
Author(s):  
Mohamed Briki ◽  
Jérôme Creuze ◽  
Fabienne Berthier ◽  
Bernard Legrand
Keyword(s):  
Phase Diagram ◽  
Monte Carlo ◽  
Phase Transitions ◽  
Monte Carlo Simulations ◽  
Bimetallic Nanoparticles ◽  
Bimodal Distribution ◽  
The Other ◽  
Nanoparticle Assembly ◽  
Interatomic Potentials ◽  
Grand Canonical

In order to build the phase diagram of Cu-Ag nanoalloys, we study a 405-atom nanoparticle by means of Monte Carlo simulations with relaxations usingN-body interatomic potentials. We focus on a range of nominal concentrations for which the cluster core remains Cu-pure and the (001) facets of the outer shell exhibit two original phenomena. Within the (N,mAg-mCu,P,T) ensemble, a structural and chemical bistability is observed, which affects all the (001) facets together. For a nanoparticle assembly, this will result in a bimodal distribution of clusters, some of them having their (001) facets Cu-rich with the usual square shape, the other ones having their (001) facets Ag-rich with a diamond shape. This bistability is replaced in the (NAg,NCu,P,T) ensemble by a continuous evolution of both the structure and the concentration of the (001) facets from Cu-rich square-shaped to Ag-rich diamond-shaped facets as the number of Ag atoms increases. For a nanoparticle assembly, this will result in an unimodal distribution of the cluster population concerning the properties of the (001) facets. This comparison between pseudo grand canonical and isothermal-isobaric results shows that the distribution of a population of bimetallic nanoparticles depends strongly on the conditions under it is elaborated.

scholarly journals Application of DSC Method in Studies on Phase Transitions of Ni Superalloys

2017 ◽  
Vol 17 (4) ◽  
pp. 133-136 ◽  
Author(s):  
R. Przeliorz ◽  
J. Piątkowski
Keyword(s):  
Phase Transitions ◽  
Specific Heat ◽  
Protective Atmosphere ◽  
Scanning Calorimetry ◽  
Heating And Cooling ◽  
Complete Melting ◽  
Calorimetric Studies ◽  
Dsc Method ◽  
Dsc Curves

Abstract The paper presents results of calorimetric studies of foundry nickel superalloys: IN100, IN713C, Mar-M247 and ŻS6U. Particular attention was paid to determination of phase transitions temperatures during heating and cooling. The samples were heated to a temperature of 1500°C with a rate of 10°C⋅min-1 and then held at this temperature for 5 min. After a complete melting, the samples were cooled with the same rate. Argon with a purity of 99.99% constituted the protective atmosphere. The sample was placed in an alundum crucible with a capacity of 0.45 cm3. Temperature and heat calibration was carried out based on the melting point of high-purity Ni. The tests were carried out by the differential scanning calorimetry (DSC) using a Multi HTC high-temperature calorimeter from Setaram. Based on the DSC curves, the following temperatures were determined: solidus and liquidus, dissolution and precipitation of the γ’ phase, MC carbides and melting of the γ’/γ eutectic. In the temperature range of 100-1100°C, specific heat capacity of the investigated superalloys was determined. It was found that the IN713C and IN100 alloys exhibit a higher specific heat while compared to the Mar-M247 and ŻS6U alloys.

A Variable-Temperature Hydrostatic Pressure Cell for Raman Scattering Experiments

1986 ◽  
Vol 40 (2) ◽  
pp. 217-223 ◽  
Author(s):  
J. J. Martin ◽  
R. Cavagnat ◽  
J. C. Cornut ◽  
M. Couzi ◽  
G. Daleau ◽  
...  
Keyword(s):  
High Pressure ◽  
Phase Transitions ◽  
Raman Scattering ◽  
Variable Temperature ◽  
Structural Phase ◽  
The Other ◽  
Structural Phase Transitions ◽  
High Pressure Cell ◽  
Pressure Cell ◽  
The One

A variable-temperature hydrostatic high-pressure cell for Raman scattering experiments is presented; it can be commonly used for pressures up to about 6 kbars, in the temperature range between 340 and 80 K. Examples of applications are given, concerning conformational equilibriums in liquid tridecane on the one hand, and structural phase transitions in crystalline (CH3)4NMnCl3(TMMC) and (CH3)4NCdCl3 (TMCC), on the other hand.

Degenerate (identity) chemical reactions in ferroelastic crystals

2019 ◽  
Vol 75 (3) ◽  
pp. 287-290
Author(s):  
Jan Fábry
Keyword(s):  
Phase Transitions ◽  
Chemical Reactions ◽  
The Other ◽  
Special Position ◽  
Definition Of

The presence of degenerate chemical reactions in crystals is discussed. They take place in some order–disorder phase transitions in crystals. The other category of identity (degenerate) chemical reactions in crystals includes a few examples of domain reorientations with simultaneous hopping of atoms/ions in some ferroelastic crystals. The product of the hopping maybe either identical with the reactant though in a different orientation or a conjugated enantiomorph. In these examples, the hopping atom is either situated in a special position or disordered about it in the paraelastic phase. The article also discusses the definition of identity (degenerate) chemical reactions which do not take into cosideration the reactions in which the reactant and the product are enantiomers or enantiomorphs.

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