Controlling the crystal structure of Ni nanoparticles by the use of alkylamines

Ni nanoparticles were prepared via thermal decomposition of nickel acetate tetrahydrate in the presence of long-chain amines, which acted as both solvents and reducing agents. By tuning the reaction temperature, Ni nanostructures with either hcp or fcc crystal structure were obtained. In principle, higher temperatures favored the formation of hcp nanoparticles. The employment of additional surfactants such as 1-adamantanecarboxylic acid and trioctylphosphine-oxide facilitated the tuning of the particles’ growth limit. The size of the particles varied between 5 and 120 nm. The magnetic features of fcc-Ni nanoparticles were quite similar to the corresponding ‘bulk’ ones. On the other hand, the hcp-Ni particles showed weak magnetic features, reflected by low magnetization values, the absence of saturation magnetization and by blocking temperatures far below room temperature.     

Competitive localization

Many problems may be cast into the form of entities utilizing resources and competing for those resources. Several models inspired by such competition have previously been shown to exhibit clumping and in some cases localization in their stable equilibrium states. We show that such localization, which we wish to call ‘competitive localization’, is generic, and we provide techniques to accurately find the equilibrium states when competitive localization occurs. We also expose some difficulties in relying on numerical simulations when exploring models of this type.     

Vibrational spectra and rotational isomerism of allyl amine

The infrared spectra of allyl amine in the vapour, liquid and solid phases have been measured from 250 to 4000 cm⁻¹. The laser-Raman spectrum in the liquid state has also been recorded photoelectrically and qualitative depolarization measurements have been made. The interpretation of the spectral data suggests the presence of two rotational isomers (‘cis and trans”, and ‘ganche and trans’) in the vapour and liquid phases whereas the form having asymmetrical structure (‘gauche and trans’, C₁ symmetry) gets stabilized in the solid state at low temperature.     

Punctuated equilibrium and power law in economic dynamics

This work is primarily based on a recently proposed toy model by Thurner et al. (2010) [3] on Schumpeterian economic dynamics (inspired by the idea of economist Joseph Schumpeter [9]). Interestingly, punctuated equilibrium has been shown to emerge from the dynamics. The punctuated equilibrium and Power law are known to be associated with similar kinds of biologically relevant evolutionary models proposed in the past. The occurrence of the Power law is a signature of Self-Organised Criticality (SOC). In our view, power laws can be obtained by controlling the dynamics through incorporating the idea of feedback into the algorithm in some way. The so-called ‘feedback’ was achieved by introducing the idea of fitness and selection processes in the biological evolutionary models. Therefore, we examine the possible emergence of a power law by invoking the concepts of ‘fitness’ and ‘selection’ in the present model of economic evolution.     

Topological and morphological transformations of developing singular paraxial vector light fields

The paper is devoted to establishment of the real-time topological and morphological dynamics of generic developing paraxial elliptic speckle fields generated and driven by the system ‘laser beam + photorefractive crystal LiNbO₃:Fe’. Generic space-time development of full gamut of polarization ellipse parameters (ellipticity, azimuth, morphology of C points, optical diabolos and handedness) and their combination in fixed beam cross-section was measured in details by the elaborated quick-action real-time Stokes-polarimetry. Whole field irreversible evolution is fulfilled through totality of random space/time C point pair nucleation/annihilation. The ‘life-story’ of C point and optical diabolo pairs is realized through ‘local topological/morphological transition’ with fully reversible scenario. It starts from smooth fragment of speckle field by formation of pre-nucleation local structure and finishes by after-annihilation local structure which decays to another smooth structure. Scenarios of star-monstar pair nucleation/annihilation and monstar  ↔  lemon transformation were established. Measured statistics of C point and diabolo morphological forms was in excellent agreement with theory predictions. All allowed scenarios of diabolo pair ‘life-story’ started/finished as star-hyperbolic monstar-hyperbolic pair were measured. Evolution of polarization ellipses handedness is implemented through L contours movement and reconnection with a saddle as the catalyst. Reconnection of L contour peninsula leads to birth of closed L contour delimiting island of fixed handedness ellipses with/without C points. Elaborated approach and presented results start the dynamic singular optics of time-dependent vector light fields.     

Non-stoichiometry and properties of ternary semiconductor phases of variable composition based on IV-VI compounds

An overview and analysis of our experimental data on the crystal structure, mechanical, thermal, galvanomagnetic and thermoelectric properties vs composition of the ternary semiconductor phases based on IV-Te compounds in the IV-X-Te systems (IV-Ge, Sn, Pb; X-Cu, Ag, Cd, In, Ga, Bi, Sb, Mn, V) are given. The separate and joint effect of deviation from stoichiometry and cation substitution on the IV-X-Te phase properties is established using the method of ‘controlled atomic defects’. Some general regularities and new physical phenomena connected with simultaneous presence of intrinsic and impurity point defects are detected. The influence of the cation substitution on the intrinsic defect equilibrium is established. It is shown that critical phenomena of percolation nature are observed in the range of small impurity contents as well as small intrinsic defect concentrations. Principally new models of the energy band structure of IV-X-Te ternary phases, which take into consideration a high concentration of non-stoichiometric defects, are proposed. The role of long- and short-range ordering is discussed. The formation of complexes as a result of chemical interaction between impurity and host atoms is detected. The above-mentioned phenomena are common for ternary phases and should be taken into account when developing materials for different applications.     

Topological phases of the two-leg Kitaev ladder

We study the phase diagram of the two-leg Kitaev model. Different topological phases can be characterized by either the number of Majorana modes for a deformed chain of the open ladder, or by a winding number related to the ‘h  -loop’ in the momentum space. By adding a three-spin interaction term to break the time-reversal symmetry, two originally different phases are glued together, so that the number of Majorana modes reduce to 0 or 1, namely, the topological invariant collapses to _Z2$Z_2$ from an integer Z. These observations are consistent with a recent general study [S. Tewari, J.D. Sau, arXiv:1111.6592v2].     

Factorised steady states and condensation transitions in nonequilibrium systems

Systems driven out of equilibrium can often exhibit behaviour not seen in systems in thermal equilibrium —for example phase transitions in one-dimensional systems. In this talk I will review a simple model of a nonequilibrium system known as the ‘zero-range process’ and its recent developments. The nonequilibrium stationary state of this model factorises and this property allows a detailed analysis of several ‘condensation’ transitions wherein a finite fraction of the constituent particles condenses onto a single lattice site. I will then consider a more general class of mass transport models, encompassing continuous mass variables and discrete time updating, and present a necessary and sufficient condition for the steady state to factorise. The property of factorisation again allows an analysis of the condensation transitions which may occur.     

Ferroelectric domains and the condensed soft mode in gadolinium molybdate

Results of lattice dynamical calculations of the high temperature phase of gadolinium molybdate (GMO) support the view that the phase transition in GMO arises from a softening of a doubly degenerate zone edge mode. We find a close correlation between the displacements associated with these soft modes and the difference in the structure of the two phases, suggesting that, at the transition one or other set of soft mode displacements is ‘condensed’, or ‘frozen in’ to the structure. On this basis we can explain the ferroelectric switching.     

On the existence of ‘l-asparagine cadmium chloride monohydrate’ crystal

It is argued that the nonlinear optical single crystal ‘l-asparagine cadmium chloride monohydrate’ grown by the slow evaporation solution growth technique by Masilamani et al. (Optik, 123 (2012) 1304-1306) is actually the well-known l-asparagine monohydrate crystal.     

Electrical and thermal studies in the commensurate incommensurate phase region of (NH4)2ZnCl4 single crystal

DC electrical conductivity for a virgin and poled annealed (NH₄)₂ZnCl₄b-axis single crystal shows a defect controlled property. A Schottky mechanism is a probable mechanism of conduction in regions of strong structural transitions. The rise of conductivity in the incommensurate and paraelectric phases is linked to an increase in discommensurations density. The activation energies (ΔE) in the three phases region were calculated. DTA measurements shows that the crystal is stable up to 200 °C and the phase transition temperatures were observed at 42, 94.8 and 137 °C. The effective activation energy (E_e) was obtained using Kissinger and Mahadevan equations. It was found to be equal to 0.49 eV. This correlates with the value obtained through DC conductivity.     

Theoretical study on the effect of dopant positions and dopant density on transport properties of a BN co-doped SiC nanotube

We investigate the effect of dopant (boron ‘B’–nitrogen ‘N’) position and density on electronic transport properties of a BN co-doped silicon carbide nanotube (SiCNT). The results show an increase in conductance when both BN impurities are far in space from each other. Orbital delocalization and appearance of new electronic states around Fermi level contribute to the current when this spacing is increased. On the other hand, a reduction in SiCNT conductivity was observed when BN dopant density was increased. This is attributed to the electronic states moving away from the Fermi level and orbital localization at higher bias voltages.     

Can a ‘magnesium sulfate admixtured l-threonine’ crystal be grown by slow evaporation solution growth method?

Slow evaporation of an aqueous solution containing l-threonine and magnesium sulphate heptahydrate, results in the fractional crystallization of the less soluble l-threonine crystal and not any novel optoelectronic ‘magnesium sulfate admixtured l-threonine’ crystal as reported by Puhal Raj et al. in Optik, 124 (2013) 6887–6891.     

Urban road network evolution mechanism based on the ‘direction preferred connection’ and ‘degree constraint’

The urban road network is a complex system that exhibits the properties of self-organization and emergence. Recent theoretical and empirical studies have mainly focused on the structural properties of the urban road networks. This research concentrates on some important parameters such as degree, average degree, meshedness coefficient, betweeness, etc. These parameters of the real road network exhibit specific statistical properties. Some studies show that perhaps these specific statistical properties are caused by a compromise mechanism of the formation of a minimum spanning tree and the greedy triangulation. Inspired by these results, we propose a principle to construct the network (we call it a MG network in this paper) whose structure is located between the minimum spanning tree and the greedy triangulation at first. The structural properties of the MG network are analyzed. We find the formation mechanism of the MG network cannot explain the urban road network evolution well. Then, based on the formation mechanism of the MG network, we add the ‘direction preferred connection’ and ‘degree constraint’ principles to the urban road network evolution simulation process. The result of the simulation network turns out to be a planar network that is in accordance with reality. Compared with the real road network’s structural properties, we find the simulation results are so consistent with it. It indicates the validation of the model and also demonstrates perhaps the ‘direction preferred connection’ and ‘degree constraint’ principle can explain the urban road network evolution better.     

Electron spectroscopy and density-functional study of ‘ferric wheel’ molecules

The Li-centered ‘ferric wheel’ molecules with six oxo-bridged iron atoms form molecular crystals. We probed their electronic structure by X-ray photoelectron and soft X-ray emission spectroscopy, having calculated in parallel the electronic structure of a single ‘ferric wheel’ molecule from first-principles by tools of the density-functional theory, using, specifically, the Siesta method. The Fe local moments were found to be 4μ_B, irrespective of their mutual orientation. Neighbouring atoms, primarily oxygen, exhibit a noticeable magnetic polarization, yielding effective spin S=5/2 per iron atom, that can get inverted as a ‘rigid’ one in magnetic transitions. Corresponding energy preferences can be mapped onto the Heisenberg model with effective exchange parameter J of about −80 K.     

Novel processing of Barkhausen noise signal for assessment of residual stress in surface ground components exhibiting poor magnetic response

The Barkhausen Noise Analysis (BNA) technique has been utilised to assess surface integrity of steels. But the BNA technique is not very successful in evaluating surface integrity of ground steels that exhibit poor micro-magnetic response. A new approach has been proposed for the processing of BN signal and two newly proposed parameters, namely ‘count’ and ‘event’, have been shown to correlate linearly with the residual stress upon grinding, with judicious choice of user defined ‘threshold’, even when the micro-magnetic response of the work material is poor. In the present study, residual stress induced upon conventional plunge surface grinding of hardened bearing steel has been investigated along with unhardened bearing steel for benchmarking. Moreover, similar correlation has been established, when primarily compressive stress is induced upon high speed grinding using cBN wheel with moderately deep cut suppressing the micro-magnetic response from the ground medium carbon steel as the work material.     

A theory of cosmic rays

We present a theory of non-solar cosmic rays (CRs) in which the bulk of their observed flux is due to a single type of CR source at all energies. The total luminosity of the Galaxy, the broken power-law spectra with their observed slopes, the position of the ‘knee(s)’ and ‘ankle’, and the CR composition and its variation with energy are all predicted in terms of very simple and completely ‘standard’ physics. The source of CRs is extremely ‘economical’: it has only one parameter to be fitted to the ensemble of all of the mentioned data. All other inputs are ‘priors’, that is, theoretical or observational items of information independent of the properties of the source of CRs, and chosen to lie in their pre-established ranges. The theory is part of a ‘unified view of high-energy astrophysics’ — based on the ‘Cannonball’ model of the relativistic ejecta of accreting black holes and neutron stars. The model has been extremely successful in predicting all the novel properties of Gamma Ray Bursts recently observed with the help of the Swift satellite. If correct, this model is only lacking a satisfactory theoretical understanding of the ‘cannon’ that emits the cannonballs in catastrophic processes of accretion.     

Estimation of the absorption coefficients of the surfaces of classrooms

Measurements of early-decay time and multivariable linear-regression techniques were used to estimate the 125-8000-Hz octave-band absorption coefficients of eight types of surfaces in university classrooms. The eight types were ‘hard surfaces’, ‘paneled surfaces’ (including hard seats and windows), ‘glued-on acoustical tiles’, ‘suspended acoustical ceilings’, ‘carpeted surfaces’, ‘upholstered seats’, ‘porous absorbers’ and ‘Helmholtz-resonator absorbers’. In general, resulting estimates were statistically significant, physically realistic and in good agreement with previous results. Values for suspended acoustical ceilings were significantly lower than published data.     

X-Ray kinetic study of glassy crystal formation in adamantane derivatives: TTT curves and crystal size effect

Abstract

The kinetics of polymorphic solid-state transformation in mixed adamantane compounds (CN_1?x Cl _x ADM: x = 0 and x = 0.25) have been studied by X-ray scattering. The classical form of the time-temperature-transformation TTT curves has been directly observed for the first time for the ordering supercooled plastic phases. For both compounds a considerable effect of crystal size on the kinetics has been observed. For x = 0.25 it leads to a continuous transition from Avrami to nucleation behaviour. These observations help us to understand the factors controlling nucleation and growth as well as to establish better operating conditions in order to form a glassy crystal.