Scissors Effect Research Articles

Mulheres na Física: a realidade em dados

Em dezembro de 2015, foi instituído pela Sociedade Brasileira de Física o Grupo de trabalho sobre Questões de Gênero (GTG), que se debruçou sobre dados envolvendo a participação de meninas e mulheres no universo da física. Dois momentos temporais distintos foram analisados: uma etapa na adolescência, quando as meninas participam das Olimpíadas Brasileiras de Física e uma etapa na vida profissional de pesquisadoras com carreiras consolidadas, que possuem bolsas de produtividade do CNPq. Com relação à primeira etapa, nossos estudos mostram claramente um declínio no percentual de meninas premiadas desde o 8° ano do ensino fundamental até o 3° no ensino médio, indicando um quadro associado ao que se chama efeito tesoura, presente antes mesmo da decisão por uma carreira científica. Com relação à segunda etapa, nossos dados mostram que o perfil dos pesquisadores bolsistas de física e astronomia é bastante semelhante no que concerne ao gênero, mas apenas um terço do percentual de mulheres pesquisadoras filiadas às Sociedade Brasileira de Física e Sociedade Astronômica Brasileira possuem bolsa, um quadro que permanece estático há mais de uma década.

Chemical scissors cut phosphorene nanostructures

Phosphorene, a recently fabricated two-dimensional puckered honeycomb structure of phosphorus, showed promising properties for applications in nano-electronics. In this work, we report a chemical scissors effect on phosphorene, using first-principles method. It was found that chemical species, such as H, OH, F, and Cl, can act as scissors to cut phosphorene. Phosphorus nanochains and nanoribbons can be obtained. The scissors effect results from the strong bonding between the chemical species and phosphorus atoms. Other species such as O, S and Se fail to cut phosphorene nanostructures due to their weak bonding with phosphorus. The electronic structures of the produced P-chains reveal that the hydrogenated chain is an insulator while the pristine chain is a one-dimensional Dirac material, in which the charge carriers are massless fermions travelling at an effective speed of light ∼8 × 105 m s−1. The obtained zigzag phosphorene nanoribbons show either metallic or semiconducting behaviors, depending on the treatment of the edge phosphorus atoms.

Bismuth alloying properties in GaAs nanowires

First-principles calculations have been performed to investigate the structural, electronic and optical properties of bismuth alloying in GaAs nanowires. A typical model of Ga31As31 nanowires is introduced for its reasonable band gap. The band gap of GaAs1-xBix shrinks clearly with the increasing Bi concentration and the band edge shifts when spin-orbit coupling (SOC) is considered. The insertion of Bi atom leads to hybridization of Ga/As/Bi p states which contributes a lot around Fermi level. Scissor effect is involved. The optical properties are presented, including dielectric function, optical absorption spectra and reflectivity, which are also varied with the increasing of Bi concentrations.

Unprecedented scissor effect of macromolecular cross-linkers on the glass transition temperature of poly(N-vinylimidazole), crystallinity suppression of poly(tetrahydrofuran) and molecular mobility by solid state NMR in poly(N-vinylimidazole)-l-poly(tetrahydrofuran) conetworks

Unexpected correlations have been found between structural parameters and glass transition temperatures (Tg) of poly(N-vinylimidazole) (PVIm) and crystallinity of poly(tetrahydrofuran) (PTHF) in a series of novel, unique PVIm-l-PTHF amphiphilic conetworks synthesized in broad composition ranges via free radical copolymerisation of VIm and semicrystalline, methacrylate-telechelic PTHF macromolecular cross-linkers with varying Mn from 2170 to 10 000 g mol−1. Differential scanning calorimetry (DSC) investigations revealed microphase separation between the covalently bonded PVIm and PTHF components, that is two distinct Tgs corresponding to the respective polymers (PVIm and PTHF) were obtained in these optically clear, transparent materials. Complete microphase separation, i.e. absence of mixed phases, was also confirmed by solid state NMR measurements. The Tg of the PVIm phase significantly decreases with increasing PTHF content, and Fox–Flory type correlation was surprisingly found between the Tg of PVIm and its Mc (average molecular weight between cross-links). This striking finding indicates a unique, unpredicted scissor effect of the macromolecular PTHF cross-linker in these materials, i.e. with respect to glass transition, PVIm behaves as individual chains between cross-links. The molecular mobility in the PVIm chain segments obtained by solid state NMR investigations shows a similar trend as a function of Mc. In the DSC thermograms, the semicrystalline PTHF has a sharp endothermic melting peak (Tm) indicating partial crystallisation of this polymer. It was found that the Tm and the crystalline fraction (Xc) of the PTHF phase are suppressed by even a minimal content of PVIm phase in the conetworks. Even complete diminishing of Xc occurs in conetworks with lower than 40 wt% PTHF of the lowest Mn (2170 g mol−1). Unexpectedly, Tm linearly decreases with Mc in conetworks with constant Mn of PTHF. These data indicate that the decrease of both Tm and Xc of PTHF is not only composition dependent, but the MW of the macromolecular PTHF cross-linker and the Mc of the PVIm component also have effects on these parameters. These results also indicate that chemical bonding of polymer chains in conetworks yields novel materials with unprecedented property variation. This provides unique opportunities for fine tuning of the investigated fundamental material properties, i.e. Tg, Tm and Xc, within certain ranges in the novel PVIm-l-PTHF amphiphilic conetworks by selecting the proper synthesis parameters, that is, composition and MW of the telechelic PTHF macromonomer cross-linker.

Revisiting the Effects of Sequence and Structure on the Hydrogen Bonding and π-Stacking Interactions in Nucleic Acids

Calculated electron densities from PBE0/6-31+G(d,p) were analyzed with respect to the hydrogen bonding within a nucleic acid base pair and the π-stacking between sets of base pairs. From published X-ray crystallographic data, base pairs were isolated from a total of 11 DNA and RNA duplexes, and their experimental geometry was maintained throughout the analyses. Focusing solely on Watson-Crick base pairs, from the values of the electron density between interacting nuclei (at the bond critical points), we provide quantitative data on individual weak interactions. For hydrogen bonding, in addition to quantifying the scissoring effect in GC base pairs, the origin of the controversy around the relative stability of AT and AU base pairs is identified and resolved. Thus, it is illustrated how the conclusion as to their relative stability rests on the specific choice of oligonucleotides compared. For π-stacking, sequence effects for tandem AT base pairs are captured, quantified, and explained, and the greater sensitivity of GC, over AT, sequences to the rise parameter is established. The results presented here show that, from experimental geometries and their electron densities, previously determined effects of the sequence and structure of a duplex on the stabilizing interactions can be captured, quantified, and traced back to the geometry of the base pairs.

Electronic Transport Calculations Using Maximally-Localized Wannier Functions

I present a method to calculate the ballistic transport properties of atomic-scale structures under bias. The electronic structure of the system is calculated using the Kohn-Sham scheme of density functional theory (DFT). The DFT eigenvectors are then transformed into a set of maximally localized Wannier functions (MLWFs) [N. Marzari and D. Vanderbilt, Phys. Rev. B 56 (1997) 12847]. The MLWFs are used as a minimal basis set to obtain the Hamitonian matrices of the scattering region and the adjacent leads, which are needed for transport calculation using the nonequilibrium Green's function formalism. The coupling of the scattering region to the semi-infinite leads is described by the self-energies of the leads. Using the nonequilibrium Green's function method, one calculates self-consistently the charge distribution of the system under bias and evaluates the transmission and current through the system. To solve the Poisson equation within the scheme of MLWFs I introduce a computationally efficient method. The method is applied to a molecular hydrogen contact in two transition metal monatomic wires (Cu and Pt). It is found that for Pt the I–V characteristics is approximately linear dependence, however, for Cu the I–V characteristics manifests a linear dependence at low bias voltages and exhibits apparent nonlinearity at higher bias voltages. I have also calculated the transmission in the zero bias voltage limit for a single CO molecule adsorbed on Cu and Pt monatomic wires. While a chemical scissor effect occurs for the Cu monatomic wire with an adsorbed CO molecule, it is absent for the Pt monatomic wire due to the contribution of d-orbitals at the Fermi energy.

Witchcraft Prosecutions and the Decline of Magic

Witchcraft prosecutions in Europe rose dramatically during the late sixteenth century, peaked in the middle third of the seventeenth century, and declined rapidly thereafter, gradually ceasing altogether by the end of the eighteenth century. The rise was driven by the dissemination of the late-medieval demonology and the “scissors effect” of rising population and constricting resources; the peak reflected the governing elite's “crisis of confidence” in the prosecutions and the demonology. The trials ended because the elite's skepticism about the magnitude of the threat posed by witchcraft gave way to disbelief in the power of magic altogether. The “crisis of confidence” manifested not only the victory of a long-standing tradition of skepticism and contemporary experience with the cruelty and injustices of the trials but also changes in popular behaviors and practices that the trials brought about. The growing acceptance of the new mechanical philosophy was less a cause than a consequence of the decline of witchcraft.

Winning The Battle Against HIV-1

Objective: To present an entirely new theory and practical solution to completely eliminate HIV-1 from the human body, based on a combination between a HAART regimen (HAART-x) and a corresponding, pre-administrated-to-(HAART-x), therapeutic vaccine (Vaccine-x) made of short HIV-1 DNA-sequences containing the point-mutations (resistance-mutations-pattern) that would be induced into HIV-1's genome by the corresponding, following, to come, HAART regimen (HAART-x). Design and methods: HIV-1's ability and need to mutate under HAART pressure is exploited, and the synergetical scissoring effect on HIV-1 of each (Vaccine, HAART)-couple is used to eradicate HIV-1 from the human body. Knowing in advance, the HIV-1 resistance mutations pattern for each antiretroviral drug, and also for any HAART or Mega-HAART regimen, (e.g. from Stanford University HIV Drug Resistance Database, http://hivdb.stanford.edu/ ), HIV-1 DNA therapeutic vaccines can be designed, produced and administrated to HIV-1 positive patients, prior to their usual, corresponding HAART regimens, and these HIV-1 DNA therapeutic vaccines prevent and hinder the emergence of drug-resistant HIV-1 (or HAART-resistant HIV-1), and thus contribute together with HAART, to the eradication of HIV-1 from the human body, and cure AIDS. Results:The general HIV-1 eradication scheme is a succession, or series, of (Vaccine-x, HAART-x)-couples: (Vaccine-1, HAART-1 ) ---> (Vaccine-2 , HAART-2) ---> (Vaccine-3 , HAART-3 ) --->........---> (Vaccine-x , HAART-x) --->........--> (Vaccine-n , HAART-n)---> Eradication and indicates that each therapeutic-vaccine (Vaccine-x) is pre-administrated to its corresponding (HAART-x) regimen. Also, each anti HIV-1 therapeutic-vaccine (Vaccine-x) is made of short HIV-1 DNA sequences which contain the pointmutations (resistance-mutations-pattern) that would be induced into HIV-1's genome by the corresponding, following, to come, HAART regimen (HAART-x). Conclusions: HIV-1 can be be eliminated from the human body, by treatment with successive (Vaccine-x, HAART-x)-couples, followed by (Vaccine-x , Mega-HAART-x)-couples

The globalisation of care: Filipina domestic workers and care for the elderly in Cyprus

Demographic trends in Europe towards an ageing population and a declining youth cohort point to a scissors effect of high demand for elderly care, but limited supplies of available labour to meet current and projected need. One market-based response by private households is the employment of immigrant women as carers. This article draws from an ethnographic study of a group of Filipina domestic workers employed as carers for elderly people in southern Cyprus, and offers insights into market care and contemporary globalisation. It points to foreign domestic workers as part of a process involving the commoditisation and transfer of important areas of reproductive labour.

Fiber Reorientation in Laminated and Woven Composites for Finite Element Simulations

A simple technique for fiber reorientation in laminated and woven composite material is presented in this paper. This technique is suitable for nonlinear finite element simulations of composite structure failure. The developed technique is implemented in the nonlinear explicit finite element code DYNA3D to demonstrate the effect of the fiber reorientation on the behavior of laminated composite materials in crash simulations. The same technique is added to a woven fabric composite material micromechanical model to account for the change of the model geometry. Using an incremental approach programmed in the MATLAB software, the stiffness change of the woven composite micromechanical model as a function of the yarn tow reorientation is investigated. Significant change in the elastic properties is observed as a result of the scissoring effect and fiber reorientation in woven fabric composites.

Competition of dark states: Optical resonances with anomalous magnetic field dependence

A different type of optical resonance has been observed in Doppler-free saturated absorption spectroscopy when the pump beam has elliptical polarization slightly deviating from the ${\ensuremath{\sigma}}^{+}$ and the probe has ${\ensuremath{\sigma}}^{\ensuremath{-}}$ polarization. An interpretation in terms of competition between two trap states and a dressed-atom model is presented. The observed extreme sensitivity of the resonance frequency to the external magnetic field is attributed to the ``scissors effect'' of the dressed states' crossing point.

Causal explanation for observed superluminal behavior of microwave propagation in free space

In this Letter we present a theoretical analysis of an experiment by Mugnai and collaborators where superluminal behavior was observed in the propagation of microwaves. We suggest that what was observed can be well approximated by the motion of a superluminal X wave. Furthermore, the experimental results are also explained by the so called scissor effect which occurs with the convergence of pairs of signals coming from opposite points of an annular region of the mirror and forming an interference peak on the intersection axis traveling at superluminal speed. We clarify some misunderstandings concerning this kind of electromagnetic wave propagation in vacuum.

Orbital interactions in stable and metastable conformations of the dimethylphosphate anion

Natural bond orbital (NBO) theory has been applied to analyze stereoelectronic preferences of the gg, tg and tt stationary states and two connecting transition states of the dimethylphosphate (DMP −) anion. In going from the compact gg to the extended tt state, the O a–P–O a angle closes as phosphoryl anionic oxygen, P–O a, bonds are weakened by negative hyperconjugation. Phosphoryl ester oxygen, P–O e, bonds are strengthened, however, due to increased π-overreach, largely a result of delocalization of ester oxygen lone pair density. In a ‘closing scissors effect’, contraction of the O e–P–O e angle between these stronger bonds also results, in this case due to the dominance of repulsive forces among the lone pairs. Counterintuitive arrangements in the transition states between gg and tg, and between two equivalent, twisted tt stationary states result, again, from dominant repulsions of oxygen lone pairs. Complexation of DMP − with water, Na +, or Mg +2 ions is accompanied by significant charge transfer to the ligand, thus imparting a degree of covalency to the anion–ligand bond. H-bonds between water and the two O a oxygens lead to delocalization of charge through lone pairs at the docking site of DMP − into σ ∗(O w–H) antibonds. For the ion-pairs, charge is transferred by a similar mechanism into Rydberg orbitals on the cation. Rearrangement of electron density within DMP − in the complexes replenishes losses from O a lone pairs and increases the magnitude of the anomeric effect involving O e lone pairs. NBO theory provides a quantitative description of the complex balance of interactions that dictate the conformational features of this biologically significant molecular functionality.

The Economics of Doctoral Education in Literature

THOUGH MY FOCUS IS ON LITERATURE, much of what I say about the economics of doctoral education also applies to the humanities and to the interpretive basic social sciences generally. Some of it is more widely relevant.' I argue that the increasing stratification of the academic workforce, with the accompanying rise of low-paid labor, results not from a cyclical economic crisis in higher education but from a chronic malaise that in the humanities at least has been with us for over a generation. The stunningly high human and financial costs of producing first PhDs and eventually tenured faculty members follow from this crisis. These costs can be moderated, but not brought under control, by programmatic reform designed to reduce time to degree and attrition rates, and by efforts to boost the number of tenure-track jobs-as important as such initiatives may be. Activism aimed against exploitation of cheap instructional labor will certainly help, but it is unlikely to be able to address the basic structural problem. Costs can be driven down more significantly only by constraining the supply of literature doctorates and expanding the demand for their services. The former is the necessary short-term strategy, the latter the preferable long-term approach. Though our highly competitive and stratified system favors the wealthier schools, most institutions possess a certain degree of flexibility. Failure to exploit this flexibility and to turn our intellectual range to account will lead not to the perpetuation of what should be viewed as an indefensible status quo but to the continued degradation of our discipline and not our discipline alone. [I The current crisis in the financing of higher education has been variously attributed to the organizational nature of the university, competition among schools, rising demand, structurally induced climbing costs, a flat budget ravaged by a shift in spending priorities and an expansion of responsibilities, and cuts in government spending out of proportion to those suffered even by other social services (Clotfelter 252-58; Gilbert et al. 3, 38-39nl; Pratt 270; Lauter 75-76). No doubt all these trends have contributed in some measure to the problem. Certainly the sudden explosion in spending at (primarily private) colleges and universities occurred in the 1980s rather than the 1990s. Real costs have escalated for decades, however. This was not an economic problem as long as tuition was low and median family income rose even more rapidly than tuition, as it did during the first twenty-five years after World War II. And it was not a political problem as long as there was broad popular support for New Deal-style public spending, as was probably the case for another decade thereafter. The double hit-economic and politicalhas damaged the financial flexibility of our line of work. The scissors effect between income and tuition reduced people's ability to pay for college. When in the second half of the 1990s that scissors effect ceased to operate for the first time in a quarter of a century, the cultural and political willingness to pay had been eroded, in part by a sustained conservative effort to defund the public sector generally and education specifically. Though humanists and especially literary critics may feel particularly under attack, the effects are experienced across the board. Even in many of the sciences, where federally funded university research expenditures have risen in recent years and will probably continue to do so, the number of qualified researchers has grown still more rapidly and other financial pressures

Simulation of stochastic dynamics in a four-body problem (computer experiment)

Abstract The results of computer experiments on modelling stochastic dynamics in a planetary four-body problem are discussed. A scissors effect in this problem was obtained. This result was first observed by the authors as a solution for a stochastic planetary four-body problem.

Thermoelastic Behavior of PEEK Thermoplastic Composite during Cooling from Forming Temperatures

In the forming of advanced thermoplastic composite structures, the stresses generated during cooling have a profound effect on the distortion and strength of the formed parts. In this paper, the thermoplastic behavior of a PEEK matrix thermoplastic composite during cooling was investigated. A procedure for determining temperature-dependent thermal expansion coefficients using off-axis composite specimens was introduced. A simple thermoplastic constitutive model was used to calculate thermal stresses during cooling. Based on this model, an explanation of a strong scissoring effect on the thermal expansion behavior of symmetric [±45] ns laminates and a calculation of warping in a non-symmetric laminate were presented

The role of oblique reflection shocks in astrophysical jets

view Abstract Citations (34) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Role of Oblique Reflection Shocks in Astrophysical Jets Hardee, Philip E. ; Norman, Michael L. Abstract Simulations of hydrodynamic slab jets show that the reflection modes predicted by the linear theory are not disruptive but saturate at finite amplitudes through the formation of weak oblique shocks. The properties of these shocks are investigated. Oblique shocks arising from the second reflection mode are weaker, propagate faster and propagate with different obliquity than oblique shocks arising from the first reflection mode. The point of intersection between first and second reflection mode shocks moves outward along the jet faster than the jet speed by a scissors effect. This simulation presents the first evidence for phase effects moving at greater than the jet's flow speed. That cylindrical astrophysical jets should contain similar features is suggested by the linear analysis and by numerical simulation of axisymmetric cylindrical jets. Implications for astrophysical jets and for apparent superluminal motions resulting from phase effects are discussed and evidence for these features in astrophysical jets is presented. Publication: The Astrophysical Journal Pub Date: July 1989 DOI: 10.1086/167629 Bibcode: 1989ApJ...342..680H Keywords: Plasma Jets; Radio Jets (Astronomy); Shock Wave Interaction; Computerized Simulation; Light Speed; Astrophysics; GALAXIES: JETS; HYDRODYNAMICS; SHOCK WAVES full text sources ADS | data products NED (3) SIMBAD (2)

Inflation or Deflation: Which Is It?

A. The concern throughout the economy and its markets stems from the scissors effect of price deflation coupled with debt inflation. After rising with the economic recovery in 1983, commodity prices peaked out in the spring of this year. Since then, all broad commodity indices have been falling off sharply. Prices of all products from aluminum to zippers have been falling, primary products and end products together. Aluminum prices dropped 35 percent in three months; that industry's depression portends a setback more severe than a mere slowdown in the economy. Copper, my favorite indicator these fifty years, plunged from 80 cents to 60 cents. Lumber prices are hitting important new lows. Gold has dropped. Oil is off and continuing to weaken. On the end products side, IBM has broken its mainframe computer prices by 18 percent and absorbed another cut as deep in the form of concessions to dealers. Bonneville cut industrial power rates by 18 percent. Newsprint is the only firm price I know. Q. But the general price indices are still moving up. That's inflation, not deflation. Consumers see prices of cars, furniture, housing rising. A. I beg your pardon. Not just key commodity prices are falling. Prices of manufactured goods that reflect real activity are falling, too. Just hang on here, I'm not talking about consumer perceptions, but about the take-home pay to the vendor. Here I see three forms of subsidynone reflected in the consumer price indices-that amount to price-cutting. We saw a price cut this week of a very important end product IBM mainframes-and a 22 percent cut in the IBM desktop computer. The second price cut takes the form of credit charges; the auto industry has relied on single-digit rates for consumer paper to move more cars than the televised Olympics could. The third is in slow payment of bills. The whole economy is on slow pay. At today's interest rates, slow pay is a calculated form of price cutting and subsidy to buyers. That means that the vendors and distributors of major products like the auto distributors are caught in the squeeze between price deflation and debt inflation at high interest rates. The slowdown in the statistical economy has been pep-

Focusing experiments with an inverse reflex tetrode

The focusing properties of an Inverse Reflex Tetrode (IRT) used for ion beam generation have been investigated experimentally. Focusing is achieved by replacing the planar (0°) electrodes of a standard IRT with moderately inwardly tapered electrodes (7.5, 10, and 15°). The greatest degree of focusing is obtained with the 15° electrodes as determined by beam profile measurements using streak photography and nuclear activation techniques at various axial target positions. A scissoring effect is observed, due to temporal variations in generator voltage and current, that is manifested by an axial variation in the focal point with time. Calculations of proton trajectories confirm the experimental results and demonstrate the importance of self-fields within the A-K gap in determining the characteristics of an ion beam generated by an IRT.

Non-spherical implosion of a dense thermonuclear plasma

In contrast to the electronic heat conduction losses which for a tamped thermonuclear micro-explosion are minimized by a spherical target shape, the adiabatic temperature rise can be larger for a non-spherical implosion geometry, whereas for a given plasma volume and density the bremsstrahlung losses are independent of the particular geometry. The enhancement of the adiabatic temperature rise results from the ‘scissors effect’ in non-spherical implosions by which a cavity wedge can assume a larger geometric implosion velocity than the physical implosion velocity of the cavity wall. The net effect of the enhanced adiabatic temperature rise by the 'scissors effect' and enhanced electronic heat conduction losses for non-spherical cavity shapes results in an optimal non-spherical implosion geometry. For the special case of an imploding oblate ellipsoid the optimal eccentricity is derived from an exact analytical solution. The predicted effect leads to a reduction in required beam power density, permitting less beam focusing than is necessary for spherical targets, which is of special importance for electron- and ion-beam induced micro-explosions, and may even make possible the attainment of thermonuclear temperatures by chemical explosives.