Anomalous thermal

Fig. 72. Linear thermal expansion of Lao 6Yo.o7Cao.33MnOj. Inset anomalous thermal expansion contribution...

In general, the cadmium halides show in their crystal structure the relation between polarizing effect and si/e of anion. The tluoride has tile smallest and least polarizable anion of Ihe lour and forms a cubic structure, while the mure polarizable heavy halides have hexagonal layer structures, increasingly covalent and al increasing distances apart in inxler down tire periodic table, in solution the halides exhibit anomalous thermal and transport properties, due primarily to the presence of complex ions, such as CDlr and CdBr r. especially in concentrated solutions or those containing excess halide ions. 

Berberet and Kaufman (Ref 121) attempted to produce ignitions with 12 MeV and 24 MeV deuterons in samples of Composition B and HMX/Exon instrumented with micro thermocouples. Ignition was achieved in both materials, but only at elevated temps. The anomalous thermal behavior indicated by the thermocouples suggested to the experimenters that a stored energy phenomenon as well as the elevated temp played an important role in the initiations. There was further evidence of an apparent dependence of the ignition on the total exposure rather than on temp... 

Neutron spectroscopy (also referred to as inelastic neutron scattering) has been used to measure the extent of guest-host interactions in a hydrate lattice, which help to explain the anomalous thermal behavior of hydrates (e.g., low thermal... 

Following the introduction to size-dependent nanophenomena presented in the previous sections, we now focus our attention on the luminescence properties of lanthanide ions at additional sites or distorted structure existing in nanophases. Phenomena of prolonged luminescence lifetime, anomalous thermalization, upconversion luminescence, dynamics of long-range interaction with two-level-systems (TLS), and quantum efficiency are to be discussed. 

We recently observed anomalous thermalization phenomena in Er +-doped Y2O2S nanocrystals of 20-nm diameter at low temperature (Liu et al., 2002). It is well known that the population of the lanthanide ions doped in the host among the energy levels generally obeys the Boltzmann distribution characterized by the Boltzmann factor. For the / th level,... 

Additional evidence of anomalous thermalization phenomena was found in the excitation spectmm 2Hn/2 4Ii5/2, 4S3/2 -> 4Ib/2 emission spectrum and upconversion excitation... 

To gain better understanding of the mechanism of anomalous thermalization in Er3"1" Y2O2 S nanocrystals, the temperature and power dependences of the luminescence intensity in excitation spectra were quantitatively studied. Integrated intensities of excitation spectra at 491.8 and 492.9 nm versus temperature (from 2.2 to 66 K) are shown in fig. 9, where each experimental point represents the integrated intensity of each main peak. The intensity of saturated hot bands in nanocrystals decreases rapidly to zero as temperature increases from 6 to 8 K, and... 

Recently, we also observed an anomalous thermalization phenomenon in Er Gd203 (1 at%) nanocrystals with diameters of 40-50 nm. In the excitation spectra at 2.9 K, hot bands originating from the upper stark level of 4Ii5/2 (38 cm-1) were observed. These hot bands disappear when temperature goes up to 5 K. Our preliminary results show that the anomalous thermalization phenomena in this system are more complicated, because they depend on the laser power and temperature. The effect of laser heating or temperature fluctuation in nanocrystals must be ruled out before a definite conclusion can be reached. 

Watase, M. and Nishinari, K. 1987a. Dynamic viscoelasticity and anomalous thermal behavioiu of concentrated agarose gels. Die Makromotekutare Chemie 188 1177-1186. 

R. Inoue, H. Tanaka, and K. Nakanishi, "Molecular dynamics simulation study on the anomalous thermal conductivity of clathrate hydrates , J. Chem. Phys. 104 (1996) 9577. 

These two methods of synthesis have led to the discovery that at compositions around x = 2, a monophase, polycrystalline NASION is very difficult to produce, even though it can be sintered to reasonable mass density ( >3.20 g/cm ) at relatively low temperatures (1100-1375°C). Unfortunately these materials contain a ZtOz second phase, possess poor mechanical strength with a low fracture toughness, have an anomalous thermal expansion behaviour, and are subject to chemical and phase instability during densification . 

Katrusiak, A. (1996d). Rigid H2O molecule model of anomalous thermal expansion of ices. 

S.U.S. Choi, Z.G. Zhang, W. Yu, F.E. Lockwood and E.A. Grulke, Anomalous thermal conductivity enhancement in nano-tube suspensions. Applied Physics Letters, 79, 2252-2254 (2001). 

The alteration of the O—H—O angle is indeed observed in structures in which the H atom becomes disordered (Katrusiak, 1992 1993). The O—H and H—O distances do not alter significantly when the H atom becomes disordered, and therefore - because of the altered O—H- - -O angle - the O- O distance decreases. This contraction of the O- O distance contributes to the thermal expansion of the crystal in such a way that a region of anomalous thermal expansion is observed in the direction of hydrogen bonds about the critical temperature (T. ) when the H atoms become disordered (Kobayashi, Uesu, Mizutani Enomoto, 1970 Katrusiak, 1993 Horvath, 1983 Horvath Kucharczyk, 1981). 

As is done in the GL-theory for a single even-parity order parameter, we write the free energy density difference between the superconducting state and the norma state as an expansion in even powers of the complex gap function A(k), which is related to the anomalous thermal average of the microscopic theory [28] where c is the electron annihilation operator with wave vector k and spin t. However, for the multiple-order parameter case we must expand A(k) as a linear combination of the angular momentum basis functions Yj(k)),... 

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