Lattice vibrations and specific heat of zinc blende

The dispersion relations, frequency distribution function and specific heat of zinc blende have been calculated using Houston's method on (1) A short range force (S. R.) model of the type employed in diamond by Smith and (2) A long range model assuming an effective charge Ze on the ions. Since the elastic constant data on ZnS are not in agreement with one another the following values were used in these calculations: {Mathematical expression}. As compared to the results on the S. R. model, the Coulomb force causes 1. A splitting of the optical branches at (000) and a larger dispersion of these branches; 2. A rise in the acoustic frequency branches the effect being predominant in a transverse acoustic branch along [110]; 3. A bridging of the gap of forbidden frequencies in the S. R. model; 4. A reduction of the moments of the frequency distribution function and 5. A flattening of the Θ- T curve. By plotting (Θ/Θ0) vs. T., the experimental data of Martin and Clusius and Harteck are found to be in perfect coincidence with the curve for the short range model. The values of the elastic constants deduced from the ratio Θ0 (Theor)/Θ0 (Expt) agree with those of Prince and Wooster. This is surprising as several lines of evidence indicate that the bond in zinc blende is partly covalent and partly ionic. The conclusion is inescapable that the effective charge in ZnS is a function of the wave vector {Mathematical expression}.

Normal vibrations of N,N-dimethylacetamide

Infrared and Raman spectra of N,N-dimethylacetamide (DMA) are recorded and the normal vibrational analysis of the DMA skeleton as well as the entire molecule carried out employing the Urey-Bradley and modified Urey-Bradley force fields. Vibrational frequencies are assigned on the basis of the normal coordinate calculations and are compared with those of related molecules. Infrared spectra of metal complexes are examined to substantiate the band assignments.

Contribution of different physical forces to the disjoining pressure of a thin water film being pressed by an oil droplet

With an objective to understand the nature of forces which contribute to the disjoining pressure of a thin water film on a steel substrate being pressed by an oil droplet, two independent sets of experiments were done. (i) A spherical silica probe approaches the three substrates; mica, PTFE and steel, in a 10 mM electrolyte solution at two different pHs (3 and 10). (ii) The silica probe with and without a smeared oil film approaches the same three substrates in water (pH = 6). The surface potential of the oil film/water was measured using a dynamic light scattering experiment. Assuming the capacity of a substrate for ion exchange the total interaction force for each experiment was estimated to include the Derjaguin-Landau-Verwey-Overbeek (DLVO) force, hydration repulsion, hydrophobic attraction and oil-capillary attraction. The best fit of these estimates to the force-displacement characteristics obtained from the two sets of experiment gives the appropriate surface potentials of the substrates. The procedure allows an assessment of the relevance of a specific physical interaction to an experimental configuration. Two of the principal observations of this work are: (i) The presence of a surface at constant charge, as in the presence of an oil film on the probe, significantly enhances the counterion density over what is achieved when both the surfaces allow ion exchange. This raises the corresponding repulsion barrier greatly. (ii) When the substrate surface is wettable by oil, oil-capillary attraction contributes substantially to the total interaction. If it is not wettable the oil film is deformed and squeezed out. (C) 2010 Elsevier Inc. All rights reserved.

Normal vibrations of N,N-dimethylacetamide

Infrared and Raman spectra of N,N-dimethylacetamide (DMA) are recorded and the normal vibrational analysis of the DMA skeleton as well as the entire molecule carried out employing the Urey-Bradley and modified Urey-Bradley force fields. Vibrational frequencies are assigned on the basis of the normal coordinate calculations and are compared with those of related molecules. Infrared spectra of metal complexes are examined to substantiate the band assignments.

Vibrational force constant and electron relaxation in H2 and Li2

The force constants of H2 and Li2 are evaluated employing their extended Hartree-Fock wavefunctions by a polynomial fit of their force curves. It is suggested that, based on incomplete multiconfiguration Hartree-Fock wavefunctions, force constants calculated from the energy derivatives are numerically more accurate than those obtained from the derivatives of the Hellmann-Feynman forces. It is observed that electrons relax during the nuclear vibrations in such a fashion as to facilitate the nuclear motions.

The Gendered Social Organisation of Defence: Two Ethnographic Case Studies in the Finnish Defence Forces

In Finland the organising of defence is undergoing vast restructuring. Recent legislation has redefined the central tasks of the Finnish Defence Forces. At the same time, international security cooperation, economic pressures and new administrative paradigms have steered the military towards new ways of organising. National defence is not just politics and principles; to a large extent it is also enacted in day-to-day life in organisations. The lens through which these realities of defence are analysed in this study is gender. How is the security sector – and national defence as part of it – organised in the changing security environment? What is the new division of labour between different societal actors in the face of security challenges? What happens ‘at work’ within the military and the defence sector more broadly? How does gender affect the way in which defence is organised and understood, and how do the changes in the organising of security affect gender relations? The thesis searches for answers to these questions in the context of two organisational settings in the male-dominated defence sector. The case study on a Finnish peacekeeping unit in the Balkans opens a critical view on men’s social practices and the everyday life of crisis management organisations. In the second case study, reorganising of provisioning in the Finnish Defence Forces turns out to be a complicated process where different power relations and social divisions intermingle. Tallberg’s extensive ethnographic fieldwork in the two focal organisations has produced a detailed set of data that lays the basis for critical analysis and policy development in terms of defence organising, cooperation around peace and security issues, and gender equality in organisations. Observations and results are provided for understanding social networks, militarisation, authority relations, care, public-private partnerships, personnel policies, career planning, and humour.

Active vibration suppression of beams with discrete actuators using optimal dynamic inversion

Most of the structural elements like beams, cables etc. are flexible and should be modeled as distributed parameter systems (DPS) to represent the reality better. For large structures, the usual approach of 'modal representation' is not an accurate representation. Moreover, for excessive vibrations (possibly due to strong wind, earthquake etc.), external power source (controller) is needed to suppress it, as the natural damping of these structures is usually small. In this paper, we propose to use a recently developed optinial dynamic inversion technique to design a set of discrete controllers for this purpose. We assume that the control force to the structure is applied through finite number of actuators, which are located at predefined locations in the spatial domain. The method used in this paper determines control forces directly from the partial differential equation (PDE) model of the system. The formulation has better practical significance, both because it leads to a closed form solution of the controller (hence avoids computational issues) as well as because a set of discrete actuators along the spatial domain can be implemented with relative ease (as compared to a continuous actuator).

A study of interactions in He2 1 in terms of the electronic forces

The He+He+1 interactions have been studied, as a function of the internuclear separation R, in terms of the electronic forces acting on the nuclei and the change in the charge distribution. The analysis reveals that at large R the atomic densities are polarized inwards, causing an attractive force on each nucleus, while at small R the difference in the nature of the interactions in the 2Σu and 2Σg systems is noted. It is seen that the He+He+1 (2Σu) interaction is less attractive than the He+1+He+1 interaction at lower values of R.

Superharmonic vibrations of order 3 in stretched strings

Superharmonic vibrations of order 3 in stretched strings driven by a single-mode planar simple-harmonic force are investigated. It is shown that planar as well as nonplanar superharmonic resonances can occur. After giving a few analytical results, the problem is thoroughly investigated numerically. The stability analysis shows that the region of stable nonplanar oscillations is much smaller than that of stable planar oscillation. It is observed in the case of nonplanar oscillations that the amplitude of the superharmonic in the plane normal to the plane of excitation is larger than that in the plane of excitation.

Stability Analysis of Composite Skew Plates Using a Dynamic Method

Stability analysis is carried out considering free lateral vibrations of simply supported composite skew plates that are subjected to both direct and shear in-plane forces. An oblique stress component representation is used, consistent with the skew-geometry of the plate. A double series, expressed in Chebyshev polynomials, is used here as the assumed deflection surface and Ritz method of solution is employed. Numerical results for different combinations of side ratios, skew angle, and in-plane loadings that act individually or in combination are obtained. In this method, the in-plane load parameter is varied until the fundamental frequency goes to zero. The value of the in-plane load then corresponds to a critical buckling load. Plots of frequency parameter versus in-plane loading are given for a few typical cases. Details of crossings and quasi degeneracies of these curves are presented.

Terahertz Time Domain Spectroscopy to Detect Low-Frequency Vibrations of Double-Walled Carbon Nanotubes

We have measured the frequency-dependent real index of refraction and extinction coefficient (and hence the complex dielectric function) of a free-standing double-walled carbon nanotube film of thickness 200 nm by using terahertz time domain spectroscopy in the frequency range 0.1 to 2.5 THz. The real index of refraction and extinction coefficient have very high values of approximately 52 and 35, respectively, at 0.1 THz, which decrease at higher frequencies. Two low-frequency phonon modes of the carbon nanotubes at 0.45 and 0.75 THz were clearly observed for the first time in the real and imaginary parts of the complex dielectric function along with a broad resonance centred at around 1.45 THz, the latter being similar to that in single-walled carbon nanotubes assigned to electronic excitations. Our experiments bring out a possible application of double-walled carbon nanotube films as a neutral density filter in the THz range.

Vibrational Spectra and Assignments for the Fundamental Vibrations of Imidazolidine-2-thione and -2-selenone

Infrared spectra of imidazolidine-2-thione (N,N?-ethylenethiourea, ETU) and its N,N?-deuterated (ETU-d2) and S-methylthiouronium iodides have been recorded from 4000 to 30 cm?1. Normal coordinate analyses of ETU and ETU-d2 have been made for all the fundamental frequencies, employing a Urey-Bradley potential function supplemented with valence type constants for the out of plane modes of the planar skeleton. Raman frequencies of ETU from literature have been utilised. The results of the vibrational analyses are discussed in relation to the group frequencies in structurally related molecules and frequency shifts on deuteration and S-methylation. The normal coordinate treatment is also performed for the planar vibrations of imidazolidine-2-selenone (N,N?-ethyleneselenourea, ESU) to propose assignments for ESU and so also to support the assignments of ETU.