Luminescence sensitivity changes in quartz as a result of annealing

Retrospective dosimetry using optically stimulated luminescence (OSL) on quartz extracted from (for example) bricks needs to account for strong OSL sensitivity changes that are known to occur depending on the previous thermal treatment of the sample. Non-heated quartz exhibits OSL orders of magnitude less per unit radiation than that for heated material. The reason these temperature-induced sensitivity changes occur in quartz is presently not well understood. This phenomenon is also seen in the related area of luminescence dating in which sedimentary quartz and quartz from heated archaeological samples show very different OSL sensitivities. In this paper we report on studies of the effects of high temperature annealing on the OSL and phototransferred TL (PTTL) signals from sedimentary and synthetic quartz. A dramatic enhancement of both OSL and PTTL sensitivity was found especially in the temperature range 500–800°C. Computer simulations of the possible effects are shown to produce data that agree in all essential details with the experimental observations. It is further demonstrated that the enhanced OSL sensitivity as a function of annealing temperature is not a pre-dose effect.     

Emergence of prime numbers as the result of evolutionary strategy

We investigate by means of a simple theoretical model the emergence of prime numbers as life cycles, as those seen for some species of cicadas. The cicadas, more precisely the Magicicadas, spend most of their lives below the ground and then emerge and die in a short period of time. The Magicicadas display an uncommon behavior: their emergence is synchronized and these periods are usually prime numbers. In the current work, we develop a spatially extended model at which preys and predators coexist and can change their evolutionary dynamics through the occurrence of mutations. We verified that prime numbers as life cycles emerge as a result of the evolution of the population. Our results seem to be a first step in order to prove that the development of such strategy is selectively advantageous, especially for those organisms that are highly vulnerable to attacks of predators.     

FeO double-well potential as a result of spin density redistribution

According to the calculation of the electron structure of the FeO molecule performed by the ZINDO1 semi-empirical technique, the ground-state adiabatic potential has two close minima, each containing one vibration level. The states of the system in this minima differ in the spatial distribution of the spin density: the spin density is centered in the iron atom in the lowest well at 1.95 Å and a fraction of the spin with the opposite sign is transferred to oxygen in the other well at 1.8 Å. The temperature dependence of the fractions of molecules with the different bond lengths in the FeO gas has been found. The probability of switching the spin states has been shown to increase with pressure and temperature.     

Emergence of semi-localized Anderson modes in a disordered photonic crystal as a result of overlap probability*

In this paper we study the effect of positional randomness on transmissional properties of a two dimensional photonic crystal as a function of a randomness parameter α (α = 0 completely ordered, α = 1 completely disordered). We use finite-difference time-domain (FDTD) method to solve the Maxwell’s equations in such a medium numerically. We consider two situations: first a 90° bent photonic crystal wave-guide and second a centrally pulsed photonic crystal micro-cavity. We plot various figures for each case which characterize the effect of randomness quantitatively. More specifically, in the wave-guide situation, we show that the general shape of the normalized total output energy is a Gaussian function of randomness with wavelength-dependent width. For centrally pulsed PC, the output energy curves display extremum behavior both as a function of time as well as randomness. We explain these effects in terms of two distinct but simultaneous effects which emerge with increasing randomness, namely the creation of semi-localized modes and the shrinking (and eventual destruction) of the photonic band-gaps. Semi-localized (i.e. Anderson localized) modes are seen to arise as a synchronization of internal modes within a cluster of randomly positioned dielectric nano-particles. The general trend we observe shows a sharp change of behavior in the intermediate randomness regime (i.e. α ≈ 0.5) which we attribute to a similar behavior in the underlying overlap probability of nano-particles.     

Biochemical and physiological changes in plants as a result of different sonic exposures

The effects of two different sonic exposures on two vegetables, namely Chinese cabbage and cucumber at two growth stages, including seedlings and mature plants were investigated. The 3 h exposures included either 20 kHz sound waves or "green music" that comprised classic music and natural sounds such as those of birds, insects, water, etc. Analysis of variance between groups (ANOVA) was used to determine the appropriate statistics parameters for the different treatments. Both exposures caused significant elevations in the level of polyamines (PAs) and increased uptake of oxygen O(2) in comparison with the controls. For Chinese cabbage the highest PAs' levels were determined for both seedlings and mature plants that were exposed to "green music". The oxygen uptake in Chinese cabbage also increased as a result of sonic exposures, and the highest oxygen uptake was also observed after "green music" treatment. For cucumber, the highest content of PAs for both seedlings and mature cucumber plants was determined as a result of 20 kHz ultrasound exposure. 20 kHz exposure of mature plants also resulted in the highest level of oxygen uptake. No statistically significant differences in the vitamin C level were determined between the different sonic treatments and sham exposed vegetables.     

Decrease in entropy as a result of measuring the time of escape from a potential well

The decrease in entropy when passing from an equilibrium thermodynamic system to a slightly nonequilibrium system is investigated. A quasi-equilibrium Boltzmann distribution is used to prove the conservation of free energy during this passage. Results are obtained for a Brownian particle in a potential well with a low escape probability. The escape is interpreted as a measurement. It is shown that because of the measurement itself, the distribution function is narrower than that for a system undisturbed by measurement, i.e., an equilibrium system. In this case, the entropy difference between the equilibrium and measurement-disturbed systems is equal to the amount of information entered into the system.     

Equilibrium melting temperature as a result of induction time measurements: Isotactic polypropylene

A method for the determination of equilibrium melting temperature from induction time measurements is suggested. Theory of the induction time, t _i (most probable period from the beginning of isothermal crystallization to the instant when a stable crystal nucleus starts growing) involves parameters that influence the nucleation-crystallization process, such as specific interfacial free-energy parameter, specific surface energies of a growing nucleus, enthalpy of crystal melting, diffusion activation energy, undercooling and the equilibrium melting temperature, T_m°. An extrapolation method exploiting the aspect of the induction time that it increases to infinity, that is, 1/t _i decreases to zero at the equilibrium melting temperature, cannot be used to calculate the equilibrium melting temperature. High- or low-temperature approximations of the basic equation yield some simplifications that make it possible to find its parameters via the best fit of the equation with experimental data. This procedure can yield also the value of the equilibrium melting temperature if the measured data are sufficiently precise. Applying that procedure to crystallization data of isotactic polypropylene, we obtained the values of the equilibrium melting temperatures 199.5°C (high-temperature approximation) and 212.7°C (low-temperature approximation). A more detailed discussion of the procedure suggests that from both these reasonable values, the higher one is more justified. This result agrees well with higher T_m° data reported in the literature.     

Quartz from southern Africa: sensitivity changes as a result of thermal pretreatment

Sensitivity changes are known to occur in quartz during luminescence measurement procedures. Accurate single-aliquot equivalent dose (D_e) evaluations can be made only if the experimental procedure applied causes no sensitivity change, or can correct for it. The quartz single-aliquot regenerative-dose (SAR) protocol developed by Murray and Wintle (Murray, A.S., Wintle, A.G., 2000. Luminescence dating of quartz using an improved single-aliquot regenerative-close protocol. Radiation Measurements 32, 57–73) incorporates a sensitivity correction procedure that was developed using measurements made on a single sample from Australia. This paper presents experimental data designed to test the applicability of this correction procedure to quartz extracted from two southern African sediments. The results indicate that accurate corrections are made using this protocol irrespective of the direction and magnitude of the sensitivity change. The implications for routine D_e evaluation are discussed.     

Formation of large craters on the earth as a result of impacts of natural cosmic bodies

The consequences of the impacts of cosmic bodies on the Earth’s surface are analyzed. The conditions of large craters formation on the solid surface of the planet are calculated using the recently introduced technique. The α-β parametric plane is used to determine the bounds for the areas in which craters with radii greater than 100 m, 1 km, and 10 km can form, where α is the ballistic coefficient and β is the mass loss parameter. The relevant areas are located at limited values of the β parameter (for small but nonzero values of the α parameter), since a solid body evaporates intensely as it moves in the atmosphere if the β values are sufficiently large. Analysis of the ranges of the α and β variations can help in prediction of catastrophic consequences of entry of cosmic bodies into the Earth’s atmosphere. The values of these parameters should be estimated before impacts with the Earth. The mass and velocity of a body entering the atmosphere seem to be the most difficult to determine a priori. However, precise astronomical observations together with the relevant software will make it possible to cope with this task.     

The Thomas-Fermi-Theory as result of a strong-coupling-limit

The energy of non-relativistic neutral atoms is shown to approach asymptotically the Thomas-Fermi-energy, when the charge of the nucleus tends to infinity.     

Selforganisation as a result of effective nonlocality

A one-component quasilinear kinetic system with nonlocal spatial coupling is considered. The long-range inhibition effect combined with a short-range activation is shown to provide a possibility of spontaneous dissipative structure formation. The effective nonlocality can be due to diffusion of an intermediate.     

Photochemistry at high temperatures – potential of ZnO as a high temperature photocatalyst

Direct conversion of solar radiation into useful, storable and transportable chemical products is the primary goal of solar chemistry. In this paper we discuss some fundamental aspects of photochemistry at elevated temperatures. We show that luminescence can serve as an indicator of the potential use of a system as a photoconverter. As an example we present experimental data on the chemical potential and on the lifetime of the excited states of ZnO. The low luminescence quantum yield together with a lifetime of about 200 ps indicate that an efficient photochemical conversion on ZnO is highly improbable. We believe this to be a general feature of chemical systems based on a semiconductor photocatalyst, in particular of photoreactions at a solid/gas interface. Received: 18 June 1996 / Accepted: 20 September 1996     

Emergence of bimodality in noisy systems with single-well potential

We study the stationary probability density of a Brownian particle in a potential with a single-well subject to the purely additive thermal and dichotomous noise sources. We find situations where bimodality of stationary densities emerges due to presence of dichotomous noise. The solutions are constructed using stochastic dynamics (Langevin equation) or by discretization of the corresponding Fokker-Planck equations. We find that in models with both noises being additive the potential has to grow faster than |x| in order to obtain bimodality. For potentials ∝|x| stationary solutions are always of the double exponential form.     

Influence of temperature on the yield of ions desorbed as a result of electron transitions: Relaxation model

A relaxation model of electron-stimulated desorption is used to investigate the influence of temperature on the yield of desorbed ions and to calculate the corresponding temperature coefficient. Experimental data on the electron-stimulated desorption of lithium and sodium ions from a tungsten surface coated with a silicon monolayer are interpreted on the basis of the theoretical results. Zh. Tekh. Fiz. 66, 109–115 (May 1997)     

Surface damage as a result of cavitation erosion

Erosion is regarded as a result of the periodic loading of a surface with spherical waves generated at the sites of the collapse of cavitation bubbles. One feature of cavitation loading is the formation of a zone of intense failure at the center of the contact surface. Damage appears a consequence of the formation of longitudinal cleavage cracks under the contact zone, which comprise a system of small annular cracks coaxial to a deep channel crack. The damage zone (blister) occupies a small fraction of the crater surface (the contact zone with the shock wave). The depth of the longitudinal cracks is an order of magnitude smaller than the thickness of the hardened layer. The hardening and erosion processes occur simultaneously. Zh. Tekh. Fiz. 68, 110–114 (September 1998)     

Stimulated emission as a result of multiphoton interference

By performing an experiment on stimulated emission by two photons in the parametric amplification process and comparing it to a three-photon interference scheme, we present evidence in support of the idea that the underlying physics of stimulated emission is simply the constructive interference due to photon indistinguishability. So the observed signal enhancement upon the input of photons can be interpreted as a result of multiphoton interference of the input photons and the otherwise spontaneously emitted photon from the amplifier.     

Damping as a result of piezoelectric energy harvesting

Systems that harvest or scavenge energy from their environments are of considerable interest for use in remote power supplies. A class of such systems exploits the motion or deformation associated with vibration, converting the mechanical energy to electrical, and storing it for later use; some of these systems use piezoelectric materials for the direct conversion of strain energy to electrical energy. The removal of mechanical energy from a vibrating structure necessarily results in damping. This research addresses the damping associated with a piezoelectric energy harvesting system that consists of a full-bridge rectifier, a filter capacitor, a switching DC–DC step-down converter, and a battery. Under conditions of harmonic forcing, the effective modal loss factor depends on: (1) the electromechanical coupling coefficient of the piezoelectric system; and (2) the ratio of the rectifier output voltage during operation to its maximum open-circuit value. When the DC–DC converter is maximizing power flow to the battery, this voltage ratio is very nearly 1/2, and the loss factor depends only on the coupling coefficient. Experiments on a base-driven piezoelectric cantilever, having a system coupling coefficient of 26%, yielded an effective loss factor for the fundamental vibration mode of 2.2%, in excellent agreement with theory.