The parameters of nonequilibrium microwave discharge in nitrogen in a tube in a rectangular waveguide

Computer codes are developed for the processing of emission spectra of nonequilibrium plasma in nitrogen for the purpose of obtaining information about the translational T _g and rotational T _rot temperatures, the populations of vibrational levels in the ground electron and electron-excited states, the electron energy distribution function, the electron concentration N _e , and the electric field intensity E. The computer codes are used to determine the parameters of microwave-discharge plasma in nitrogen in discharge systems of two types, namely, in a discharge tube (with a radius of 1 cm), which crosses a rectangular waveguide (plasmatron on the H ₁₀ wavelength, at a pressure of 1.7 torr and absorbed power density of 1.5 W/cm³), and in a discharge section of similar structure on the basis of prismatic resonator (at a pressure of 1.0 torr and absorbed power density of 0.4 W/cm³). The mechanisms of population of the N₂(C ³Π_u) state are treated.     

Structural changes in S&T research in India

Before India became an independent country, its scientists and policy makers could foreseethe importance of science in its development, and accordingly a number of research anddevelopment (R&D) institutions were established. However during these five decades ofindependence, the choice between basic sciences and technology was always a subject of debate.It will be appropriate now to examine the changing patterns of Science and Technology (S&T)manpower growth to find out the ground truth reality. The present study pertains to the analysis ofS&T outturn data in various fields of scientific research that can provide a base for S&T planningand policy making. These S&T indicators will be helpful in estimating future requirements, whichin turn can be useful to a great extent in science and technology policy formulation. Theseestimates and future projections are based on mathematical modelling of the data pertaining to theoutturn of highly qualified Scientific and Technical (S&T) personnel in India from differentfaculties over the period 1990-1998. From the trend analysis it is evident that research is no moreperceived as an interesting career except in the field of engineering and medicine. The findingsfurther suggest that there is a noticeable shift from basic sciences to technology.     

Bose-Einstein Condensation in Liquid 4He in Vycor

We present neutron scattering measurements of Bose-Einstein condensation (BEC) in liquid ⁴He confined in Vycor. The data show clear evidence of a condensate in Vycor with a condensate fraction comparable to that of bulk superfluid ⁴He, approximately 7.5% at low temperature and SVP. The temperature dependence of n₀(T) is also similar to that in the bulk with critical temperature for BEC, T_BEC, in the range 1.80BEC<2.05 K. The data are not accurate enough to show whether T_BEC for Vycor is the same or greater than the depressed critical temperature for superfluidity, T_c=1.95 K.     

Crack growth in structural adhesive joints in aqueous environments

The adhesive fracture energy, G _c , of metallic joints, bonded with a rubber-toughened epoxy adhesive, has been measured using monotonically-loaded tests. Such tests have been conducted in various relative humidities and in water, at 21 °C. Two surface pretreatments have been employed for the substrates prior to bonding: a simple grit-blast and degrease (‘GBD’) pretreatment or a grit-blast, degrease and silane primer (‘GBS’) pretreatment. The joints were formed using metallic substrates which were either (a) aluminium-alloy substrates, (b) steel substrates, or (c) ‘dissimilar’ substrates (i.e. one substrate being aluminium-alloy with the other one being steel). For both test environments, when G _c was plotted against the crack velocity, three regions of fracture behaviour could be distinguished. At low rates of displacement the crack grew in a stable manner, visually along the interface, and relatively low crack velocities could be readily measured. This was termed ‘Region I’ and here the value of G _c measured in the aqueous environment was relatively low compared to that measured in a relatively dry environment of 55% relative humidity. On the other hand, at relatively high rates of displacement the crack always grew in a stick-slip manner mainly cohesively in the adhesive layer at approximately 20 km/min. This was termed ‘Region III’, and here the value of G _c was relatively high and independent of the environmental test conditions employed. In this region the crack was considered to grow faster than the water molecules were able to reach the crack tip, which explains the independence of G _c upon the test environment. In between ‘Region I’ and ‘Region III’, a transition region was observed which was designated as ‘Region II’. The major effect of the ‘GBS’ pretreatment, compared to the ‘GBD’ pretreatment, was to increase the value of G _c both in ‘Regions I and III’, although the presence of the silane primer had the far greater effect in ‘Region I’.     

Vortices in superconductors

In type II superconductors where the London penetration depthλ is larger than the coherence lengthξ, there is a possibility of flux penetration inside the sample for magnetic field greater than \(H_{0_1 } \left( { = \frac{{\phi _0 }}{{4\pi \lambda ^2 }}ln \lambda /\xi , \phi _0 = \frac{{hc}}{{2e}}} \right).\) The flux penetrates in the form of vortices with core of sizeξ. However these vortices differ from those in superfluid He⁴ in variation of currentj(r) circulating around them. For superconductorsj(r) ～ 1/r only up to a distanceλ and then it falls exponentially whilev(r) ～ 1/r for all distances in superfluids. The reason is that in superconductors vortex carries a magnetic flux which is screened by conduction electrons. This coupling of order parameter field (the pairing wavefunction) with the gauge field has many interesting implications for superconductors and for non-Abelian gauge theories. Some examples are as follows:

1. The energy of the vortices is reduced. The energy of vortex of lengthL (ind = 3 sample) is of orderL lnL for a superfluid, is of orderL in a superconductor, and (in ad = 2 sample) the energy of a vortex point which diverges like lnR (whereR is the size of the sample) in a superfluid becomes finite in a superconductor.
2. The superconducting-normal transition in three dimension is very weak first order, because the fluctuations of the gauge field, when summed over, add to Ginzburg Landau free energy a term proportional to |ψ|³, whereψ is the order parameter.
3. Because of the lnr behaviour of interaction energy of vortices, a two-dimensional superfluid sample can exhibit a Kosterlitz-Thouless type transition whereas a strictlyd = 2 superconductors should not have any. However for dirty superconducting films whereλ is large vortex binding-unbinding transition can be observed with quite a rich phase diagram.

The paper presented at the discussion meeting discusses the above in detail. Here we give only a brief summary of results and some relevant references.     

The diorama in great Britain in the 1820s

Abstract

L. J. M. Daguerre (1787-1851), originally a stage designer and scene painter,¹ in April 1821 formed a partnership with Charles Bouton (1781-1853) to develop a ‘Diorama’ in Paris. As Helmut and Alison Gernsheim have said in their account of the Diorama in L.J.M. Daguerre: The History of the Diorama and the Daguerreotype, it was ‘an ideal collaboration, each gaining much from the other's exoerience’. Bouton was the more exoerienced and distingulshed painter, Daguerre the greater expert in lighting and scenic effects.²     

Feshbach Shape Resonance in Multiband Superconductivity in Heterostructures

We report experimental data showing the Feshbach shape resonance in the electron doped MgB₂ where the chemical potential is tuned by Al, Sc, and C substitutions. The scaling of the critical temperature T _c as a function of the Lifshitz parameter z = E _Γ−E _F, where E _F is the chemical potential and E _Γ is the energy of the Γ critical point where the σ Fermi surface changes from the 3D to a 2D topology, is reported. The resonant amplification of T _c(z) driven by the interband pairing is assigned to a Feshbach shape resonance characterized by quantum superposition of pairs in states corresponding to different spatial location and different parity. It is centered at z = 0 where the chemical potential is tuned to a Van Hove-Lifshits feature for the change of Fermi surface dimensionality in the electronic energy spectrum in one of the subbands. In this heterostructure at atomic limit the multiband superconductivity is in the clean limit because the disparity and negligible overlap between electron wavefunctions in different subbands suppresses the single electron interband impurity scattering rate. The emerging scenario from these experimental data suggests that the Feshbach shape resonance could be the mechanism for high T _c in particular nanostructured architectures.     

Langsames Ermüdungsrisswachstum in Aluminium‐ und Magnesiumgusslegierungen in Raumluft und in Vakuum

Slow fatigue crack growth in aluminium and magnesium cast alloys in ambient air and in a vacuum The influence of ambient air on near threshold fatigue crack growth in the magnesium cast alloys AZ91 hp, AM60 hp and AS21 hp and in the aluminium cast alloy AlSi9Cu3 has been investigated. Fatigue crack growth properties at a cycling frequency of 20 kHz in ambient air and in a vacuum are significantly different. In a vacuum, the threshold stress intensity amplitude of the aluminium alloy is 30% higher than in ambient air, and the threshold values of the magnesium alloys in a vacuum are up to 85% higher than in ambient air. Moisture of ambient air is responsible for accelerated crack growth at growth rates below 1–3 × 10⁻⁹ m/cycle (AlSi9Cu3) and 2–5 × 10⁻⁸ m/cycle (magnesium alloys), respectively. In ambient air a minimum crack growth rate of 5 × 10⁻¹¹ − 2 × 10⁻¹⁰ m/cycle was observed, whereas far lower minimum growth rates were found in a vacuum.     

Trends in Russian research output in post-Soviet era

Recently, the Russian government has ordered evaluation and reform of the basic research system. As a consequence, the number of research staff at the Russian Academy of Sciences will be reduced by 20% by 2007. The basis for research evaluation and institute budgeting will be bibliometric indicators. In view of these changes we look at the Russian publication output and argue that

Bose-Einstein Condensation in Multilayers

The critical BEC temperature T _c of a non interacting boson gas in a layered structure like those of cuprate superconductors is shown to have a minimum T _c,m , at a characteristic separation between planes a _m . It is shown that for a<a _m , T _c increases monotonically back up to the ideal Bose gas T ₀ suggesting that a reduction in the separation between planes, as happens when one increases the pressure in a cuprate, leads to an increase in the critical temperature. For finite plane separation and penetrability the specific heat as a function of temperature shows two novel crests connected by a valley in addition to the well-known BEC peak at T _c associated with the 3D behavior of the gas. For completely impenetrable planes the model reduces to many disconnected infinite slabs for which just one hump survives becoming a peak only when the slab widths are infinite.     

Participation of helium in discontinuous transformations in metallic alloys

Abstract

The influence of helium on the diffusion at a migrating boundary has been investigated during discontinuous precipitation in a Co–14 at.-%Al alloy and during discontinuous dissolution in an Al–15 at.-%Zn alloy. The helium was introduced into the alloys via a plasma treatment using various fluxes. Two opposing processes have been observed depending on the flux. One, below a critical flux, led to an increase in the linear growth rate of discontinuous precipitation and discontinuous dissolution owing to an enhanced concentration of vacancies, which acted as carriers of solute atoms in the diffusion process. The other process, above the critical flux, resulted in the appearance of helium bubbles, which acted as mechanical obstacles to the moving discontinuous precipitation and discontinuous dissolution front and as sinks for the excess vacancies. The effect of helium on the diffusion ahead of the advancing front during discontinuous precipitation and discontinuous dissolution has been well described using a parameter D_b^{Al or Zn}/D_V^He proposed by the authors.

MST/1531     

Kinematical transformations in amorphous selenium alloys used in xerography

Differential scanning calorimetric (DSC) studies were carried out on xerographic photoreceptor materials of amorphous selenium (a-Se), a-Se_1&#x2203-xTe_x and a-Se:0.5 wt% As alloys with various amounts of chlorine doping. Glass transformation kinetics of bulk and vapour-deposited film samples were essentially identical indicating a similar amorphous structure for both forms. The glass transition temperature,T _g, in the a-Se_1&#x2203-xTe_xsystem was found to increase monotonically with the tellurium content up to 13 wt% which was accompanied by a fall in the activation energy,E _gl, for the structural relaxation. 0.5wt% As increasedT _g, whereas chlorine doping in the amounts used (100 ppm) had no effect onT _g. Crystallization exotherms were analysed using the Kissinger method which was shown to remain a valid analysis by integrating the fundamental Kolmogoroff equation describing crystallization transformations by nucleation and growth. The signifiance of the activation energy,E _A, and the frequency factor,C ₀, in the Kissinger analysis is discussed and used in interpreting the different crystallization behaviour exhibited by the various alloys. The apparent activation energy,E _A, of the crystallization kinetics was found to fall with the temperature range accessed in the DSC experiment. When other authors' previous crystallization studies by other methods were also considered, then 1/E _A was found to fall nearly linearly with the mean reciprocal temperature, 1/T, used in the experiment. It is argued that this behaviour arises if the crystal growth rate scales with the inverse viscosity of the melt and the latter is described by a Vogel-Tammann-Fulcher type of behaviour. The additives tellurium and arsenic retard the crystallization essentially by increasing the viscosity. Chlorine doping was also found to have an inhibitory effect but due probably to a change in the nucleation kinetics, rather than a viscosity rise.     

Magnetotransport in field-induced spin density waves in Bechgaard salts

We study theoretically the electrical conductivity in a field-induced spin density wave (FISDW) in Bechgaard salts in a high magnetic field. We find a new contribution to the Hall conductivity, which appears only in a FISDW withN0. Furthermore, this Hall conductance has an activated form with an energy gap ₀ at low temperatures, unlike the quantum Hall effect. Therefore, the present theory predicts that the Hall resistance increases exponentially at low temperatures, which can be tested experimentally.On leave of abence from Nankai University, China.     

Textures in narrow cylinders in superfluid 3He-A

We calculate the equilibrium configurations of three textures in a narrow cylinder in the presence of superflow along the cylinder axis. The Mermin-Ho texture is shown to be unstable against a small twist in the dipole-free limit even in the absence of superflow. The radial disgyration undergoes a second-order transition forqR -3.31, while the circular disgyration gives rise to a helical texture forpR 3.5, whereR is the radius of the cylinder andq [ (2m/)V _s]andp are momenta associated with superflow. The associated nuclear magnetic resonance frequencies are determined.The present work was supported by the National Science Foundation under Grant No. DMR-76-21032.     

Plasma density in discharge sustained in inhomogeneous gas flow by high-power radiation in the terahertz frequency range

We have measured the density of plasma (electron concentration) in discharge maintained in inhomogeneous argon flow under the action of high-power pulsed radiation of gyrotron (frequency, 0.67 THz; power 40 kW; pulse duration, 20–30 μs) in a range of background gas pressures in the discharge chamber from 10^–3 to 300 Torr. The electron concentration at low pressures (10^–3 to 7 Torr) was determined using Starkeffect induced broadening of the H_α atomic emission line (656.3 nm) of hydrogen present in discharge as a small impurity in residual gases. The maximum observed Stark broadening of the H_α line corresponded to a plasma density on the order of 2 × 1016 cm^–3, which exceeded the critical value for the given frequency of radiation sustaining the discharge. At background pressures above 7 Torr, the plasma density was estimated from analysis of the spatiotemporal patterns and waveforms of discharge glow in the visible spectral range. These estimations gave electron concentrations on the level of (1–2) × 10¹⁵ cm^–3.     

Losses in superconducting cables in pulsed magnetic fields

Measurements have been carried out of superconducting cables of different types in pulsed magnetic fields. Three types of samples have been made from multifilamentary Nb_0.5  Ti_0.5 superconductors: one, a cluster of isolated wires; two, a double-layer twisted flat cable; and three, one-layer twisted tube samples. Dependences have been studied of ac losses on the amplitude, direction and change velocity of the magnetic field as well as on the diameter of filaments and twist pitch. It is shown that the ac losses in unsoldered samples are close to those in the cluster of isolated wires.     

Education in sustainable production in US universities

The evolution and current status of sustainable production education (SPE) in the United States is reviewed, both as a discrete entity and as an intersection of multiple disciplines. This paper (a) examines the current array of compatible and conflicting theories that guide the alternative approaches to SPE, (b) reviews the wide array of applications to which such theories and associated methodologies have been applied, and (c) presents a case study of the emerging interdisciplinary approach to SPE at Purdue University in West Lafayette, Indiana, USA, and its network of national and international collaborators. North Atlantic Treaty Organization (NATO) Committee on the Challenges to Modern Society (CCMS). Pilot study on clean products and processes Annual meeting, May 2–6, 2004, Budapest, Hungary

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Polar nanoclusters in relaxors

The central problem in the physics of relaxors is the nature of the polar nanoclusters. Whereas relaxors are homogeneous at high enough temperatures, polar nanoregions immersed in a neutral matrix are formed below a certain temperature T _b . This should lead to a two component system. Here we present direct microscopic evidence for the two component nature of relaxors. We show that the chemical shift perturbed ²⁰⁷ Pb NMR spectra of these systems consist of an isotropic component corresponding to a spherical glassy matrix which does not respond to an applied electric field, and an anisotropic component, corresponding to frozen out polar nanoclusters which order in a strong enough electric field, forming a ferroelectric phase. This is as well reflected in the dynamic properties where the relaxation time distribution function starts to become asymmetric with decreasing temperature and a second maximum—which is never seen in dipolar glasses and is obviously due to polar clusters—appears on further cooling. We also show that the basic difference between dipolar glasses and relaxors is the fact that polar nanoclusters can be oriented in a strong enough electric field and a ferroelectric phase can be induced. This is not the case in dipolar glasses where the response is due to single dipoles which can not be ordered by applied electric fields.     

Field-Induced Superconductivity in MoS2

Semiconducting TMDs are nowadays attracting great interest after the invention of the so-called “Scotch-tape method” established in graphene research. Semiconducting TMDs are front-runners of “post graphene” materials for their finite band gap crucial for device applications. MoS₂ is the most widely used TMD because of its application as a solid lubricant. Scientifically, it shows superconductivity after alkali or alkaline-earth doping with a highest T _c of around 7 K. Recently, we succeeded in inducing superconductivity in the MoS₂ transistor adopting electric double layer (EDL), a nanosized capacitor, as a gate dielectric. The field-induced superconducting transition of MoS₂ was realized with a maximum T _c around 11 K, the highest not only within a reported MoS₂ compound, but also among TMDs. This highest T _c lies in the carrier density region much smaller than a chemically doped compound; a low density region has never been successfully accessed by chemical methods. Combining a HfO₂ (high-k) back gate, quasi-continuous control of carrier density, and thus quantum phase, was demonstrated to unveil the phase diagram; the T _c exhibits strong carrier density dependence with a superconducting dome. Our result implies a common existence of the superconducting dome in 2D band insulators.     

Collective modes and sound propagation in a magnetic field in superfluid3He-B

A high-resolution, ultrasonic (12–89 MHz) acoustic impedance technique has been used to investigate the order parameter collective modes in superfluid³He-B over a pressure range of 0–15 bar and in magnetic fields up to 180 mT. In agreement with earlier experiments, theJ=2 real squashing mode has been observed to split into five components in small magnetic fields. However, contrary to earlier theoretical estimates, the Zeeman shifts have been found to become extremely nonlinear as the magnetic field is increased. The extent of this nonlinearity is largest at low pressures and at temperatures close toT _c. In comparison with recent theoretical work, the nonlinear Zeeman shifts may be explained as a result of two effects. First, there is a significant distortion of the B-phase energy gap in large magnetic fields. Second, there is an important coupling between the sameJ _zsubstates of the differentJ modes. In this sense the nonlinear evolution of the real squashing mode constitutes the observation of the Paschen-Back effect in³He-B. A comparison of the observed Zeeman shifts with theoretical expressions has yielded information about particle-particle and particle-hole interaction effects in the superfluid. In the limitT 0 and above a threshold field, the real squashing mode has been found to possess additional structure. TheJ _z=0 substate has been observed to split into a doublet. The separation between the two components of the doublet is of the order of 100–200 kHz and remains independent of the magnetic field. The origin of the doublet may be understood in terms of a recent theory which postulates a texture-dependent collective mode frequency. Further, at extremely small fields the effects due to dispersion of the real squashing modes have been found to be important. The magnitude of the dispersion-induced mode splitting in zero field is found to be consistent with theoretical predictions. TheJ=2 squashing mode has also been studied in the presence of a magnetic field. TheJ _z=0 state of the squashing mode is observed to shift to lower temperatures in a magnetic field. An additional field dependence of the observed acoustic impedance is interpreted as the evolution of theJ _z=–1, –2 states, but appears to be inconsistent with theoretical predictions.