Miracle-dz/UniFAR-FTUs huggingface dataset:
IRP (interference rejection processor) revisited—A new approach to multiple‐interference rejection and elimination of beam pattern distortion

An algorithm is presented that enables rejection of an arbitrary number of interfering sources at an array with no distortion or sidelobe degradation of the array beam pattern. The algorithm is an extension of the earlier interference rejection processor (IRP) algorithm, which is a well‐known method for rejecting single‐interference sources. Rejection of two interfering sources by ∼40 to 50 dB with no beam pattern distortion is demonstrated in a computer experiment using simulated data.
Symmetry breaking and the random-phase approximation in small quantum dots

The random-phase approximation has been used to compute the properties of parabolic two-dimensional quantum dots beyond the mean-field approximation. Special emphasis is put on the ground state correlation energy, the symmetry restoration, and the role of the spurious modes within the random-phase approximation. A systematics with the Coulombic interaction strength is presented for the 2-electron dot, while for the 6- and 12-electron dots selected cases are discussed. The validity of the random-phase approximation is assessed by comparison with available exact results.
Particle creation in the Bell - Szekeres spacetime

The quantization of a real massless scalar field in a spacetime produced in a collision of two electromagnetic plane waves with constant wavefronts is considered. The background geometry in the interaction region, the Bell - Szekeres solution, is locally isometric to the conformally flat Bertotti - Robinson universe filled with a uniform electric field. It is shown that before the waves interact the Bogoliubov coefficients relating different observers are trivial and no vacuum polarization takes place. In the non-singular interaction region neutral scalar particles are produced with the number of created particles and spectrum typical of gravitational wave collision.
A controlled comparison of teaching methods in first-year university physics

Abstract This study presents a rigorous comparison between two teaching methods currently used in the first year of university-level physics programmes. Two groups of year 12 and 13 school students, aged between 16 and 18 years old, were given a short lecture course on elementary Newtonian Mechanics, one group attending more traditional passive-student lectures and the other attending an interactive active-student programme. The two groups were constructed to be as similar as possible in terms of relevant factors and were pre-tested with the Force Concept Inventory (FCI) and post-tested with the FCI and the Mechanics Baseline Test (MBT). Several measures of learning based on pre-test/post-test score change were employed to assess the relative effectiveness of the two lecture styles. The principal result of this study was the early onset of greater learning gains among students in the active-student programme compared to students in the passive-student programme. The particular choice of learning gain metric affected the interpretation of our results. We resolved this issue using a generalization of the normalized learning gain. Using this measure we also found improvement in problem-solving skill among females in the active-student group, but not in the passive-student group. On the other hand, males showed improvement in problem-solving skill in the passive-student group but not the active-student group.
Superfluidity or supersolidity as a consequence of off-diagonal long-range order

We present a general derivation of Hess-Fairbank effect or nonclassical rotational inertial (NCRI), i.e., the refusal to rotate with its container, as well as the quantization of angular momentum, as consequences of off-diagonal long-range order (ODLRO) in an interacting Bose system. Afterwards, the path integral formulation of superfluid density is rederived without ignoring the centrifugal potential. Finally and in particular, for a class of variational wave functions used for solid helium, treating the constraint of single-valuedness boundary condition carefully, we show that there is no ODLRO and, especially, demonstrate explicitly that NCRI cannot be possessed in absence of defects, even though there exist zero-point motion and exchange effect.
Extremely Massive Quasars Are Not Good Proxies for Dense Environments Compared to Massive Galaxies: Environments of Extremely Massive Quasars and Galaxies

Black hole mass scaling relations suggest that extremely massive black holes (EMBHs) with MBH ≳ 109.4 M⊙ are found in the most massive galaxies with Mstar ≳ 1011.6 M⊙, which are commonly found in dense environments, like galaxy clusters. Therefore, one can expect that there is a close connection between active EMBHs and dense environments. Here, we study the environments of 9461 galaxies and 2943 quasars at 0.24 ≤ z ≤ 0.40, among which 52 are extremely massive quasars with , using Sloan Digital Sky Survey and MMT Hectospec data. We find that, on average, both massive quasars and massive galaxies reside in environments more than ∼2 times as dense as those of their less massive counterparts with . However, massive quasars reside in environments about ∼2 times less dense than inactive galaxies with , and only about one third of massive quasars are found in galaxy clusters, while about two thirds of massive galaxies reside in such clusters. This indicates that massive galaxies are a much better signpost for galaxy clusters than massive quasars. The prevalence of massive quasars in moderate to low density environments is puzzling, considering that several simulation results show that these quasars appear to prefer dense environments. Several possible reasons for this discrepancy are discussed, although further investigation is needed to obtain a definite explanation.
Jamming, Force Chains, and Fragile Matter

We consider materials whose mechanical integrity is the result of a jamming process. We argue that such media are generically ``fragile,'' unable to support certain types of incremental loading without plastic rearrangement. Fragility is linked to the marginal stability of force chain networks within the material. It can lead to novel mechanical responses that may be relevant to (a) jammed colloids and (b) poured sand. The crossover from fragile to elastoplastic behavior is explored.
Heaviest Nuclei from 48Ca-induced Reactions

The observation of atomic numbers Z by 40% larger than that of Bi, the heaviest stable element, is an impressive extension in nuclear survival. Although the super heavy nuclei (SHN) are at the limits of Coulomb stability, shell stabilization lowers the ground-state energy, creates a fission barrier, and thereby enables the SHN to exist. The fundamentals of the modern theory concerning the mass limits of nuclear matter have thus obtained experimental verification.
Warwick-Monash Economics Student

The impact of teachers’ unions on educational outcomes is theoretically and empirically ambiguous. This study aims to provide additional evidence to this debate by analyzing the educational impact of Wisconsin’s Act 10, which significantly weakened teachers’ unions. A unique school-level dataset is constructed containing data on educational outcomes, high-school and district-level characteristics in Wisconsin and Illinois. Schools in treated and control groups are matched using propensity score matching. A difference-in-difference methodology is used to mitigate problems surrounding simultaneity and omitted variable bias from standard OLS regression. This paper uses an event study design and a triple difference model to estimate the effect of Act 10 on the dropout rate and subject proficiency rate. The triple difference model used has lower power but is more robust to the parallel trends assumption as it takes into account differences in economic conditions between states. Models suggest that weakening teachers’ unions worsens educational outcomes, providing support for the union-voice hypothesis. This study employs an event study design and triple difference model to estimate the effect of Act 10 on educational outcomes. The necessary identification assumption for the event study design is one of parallel trends, which requires that public schools in Wisconsin would have followed the same trend in educational outcomes as public schools in Illinois if Act 10 never occurred. The triple difference model controls for economic differences between states and is more robust to this parallel trends assumption, relying only on parallel trends in relative outcomes for public and charter schools in Wisconsin and Illinois. Results are robust to matching and are not driven by changes in student composition. and propensity matching to generate more valid control group. 2006-2015. A difference-in-difference methodology is used to mitigate problems surrounding simultaneity and omitted variable bias from standard OLS regression and propensity score matching is used to create a more valid control group. The triple difference model used has lower power but is more robust to the parallel trends assumption as it takes into account differences in economic conditions between states. This paper provides evidence that weakening teachers’ unions can have a negative impact on the student dropout rate and test scores, supporting the union-voice hypothesis. Differences in model findings can be reconciled by within-state spillover effects where good teachers in Wisconsin left public schools due to Act 10. The negative impact of Act 10 on educational outcomes is consistent with Baron (2018) which increases confidence in the results.
Observations of gravity–capillary lump interactions

In this experimental study, we investigate the interaction of gravity–capillary solitary waves generated by two surface pressure sources moving side by side at constant speed. The nonlinear response of a water surface to a single source moving at a speed just below the minimum phase speed of linear gravity–capillary waves in deep water ( $c_{min}\approx 23~\text{cm}~\text{s}^{-1}$ ) consists of periodic generation of pairs of three-dimensional solitary waves (or lumps) in a V-shaped pattern downstream of the source. In the reference frame of the laboratory, these unsteady lumps propagate in a direction oblique to the motion of the source. In the present experiments, the strengths of the two sources are adjusted to produce nearly identical responses and the free-surface deformations are visualized using photography-based techniques. The first lumps generated by the two sources move in intersecting directions that make a half-angle of approximately $15^{\circ }$ and collide in the centreplane between the sources. A steep depression is formed during the collision, but this depression quickly decreases in amplitude while radiating small-amplitude radial waves. After the collision, a quasi-stable pattern is formed with several rows of localized depressions that are qualitatively similar to lumps but exhibit periodic amplitude oscillations, similar to a breather. The shape of the wave pattern and the period of oscillations depend strongly on the distance between the sources.
CRYSTAL-ORIENTATION EFFECTS ON THE PIEZOELECTRIC FIELD AND ELECTRONIC PROPERTIES OF STRAINED WURTZITE SEMICONDUCTORS

Crystal orientation effects on the piezoelectric field and electronic properties of strained GaN bulk semiconductors are investigated. Analytical expressions for the band gap, wave function, and momentum matrix element of strained wurtzite GaN using a recently derived block-diagonalized Hamiltonian are shown. We find that the energy separation between the top two valence bands increases with the angle \ensuremath{\theta} between the growth ${(z}^{\ensuremath{'}})$ direction and the c axis. This results in a significant reduction of the effective mass of the top valence band along the transverse ${(k}_{x}^{\ensuremath{'}})$ direction with increasing angle for both compressively and tensilely strained GaN crystals. Similar results are observed in the valence-band dispersion relations for the quantum-well (QW) structure. The dispersion curves for the QW structure also show a lifting of the Kramers degeneracy due to the piezoelectric field, which causes an asymmetry in the potential. We find that the optical matrix element of the TE polarization between the conduction (C) and heavy hole (HH) bands of the compressively strained GaN for a growth direction with $\ensuremath{\theta}g~30\ifmmode^\circ\else\textdegree\fi{}$ is about twice as large as that of the (0001) orientation $(\ensuremath{\theta}=0\ifmmode^\circ\else\textdegree\fi{}). $ The piezoelectric polarizations of the compressive and tensile strains are plotted as a function of the growth direction. The crystal orientation at which a maximum polarization occurs is shown as a function of strain. In particular, the GaN crystal along the $(101\ifmmode\bar\else\textasciimacron\fi{}0)$ growth direction $(\ensuremath{\theta}=90\ifmmode^\circ\else\textdegree\fi{})$ shows zero normal piezoelectric polarization ${(P}_{z}^{\ensuremath{'}})$ for the compressive and tensile strains. These results show that crystal orientation dependence of the piezoelectric field and strain significantly affect the electronic transport properties as well as optical interband absorption properties.
Chiral symmetry and the pion gas virial expansion

In this work we study the thermodynamic properties of the pion gas starting from the realistic elastic scattering phase shifts obtained from chiral perturbation theory and using the virial expansion. In particular we study the equation of state and the behavior of the quark condensate as a function of the temperature and the density. {copyright} {ital 1998} {ital The American Physical Society}
Effects of humidity on stress in thin silicon dioxide films

The stresses of thermally grown as well as chemically vapor deposited (CVD) silicon dioxide were measured by the cantilever beam technique using x‐ray diffraction. Thermally grown oxide shows reversible stress changes upon heating or cooling of the films. The linear thermal expansion of such films is similar to that of bulk vitreous silica, 5×10−7 °C−1, the biaxial elastic modulus was found to be 6.3×1011 dyn/cm2. CVD oxides show extensive hysteresis in the stress‐temperature curves when tested in ambient air. From stress measurements of such films, deposited on Si and GaAs, it was concluded that their average linear thermal expansion coefficient in the temperature range of −170–115 °C is 4×10−6 °C−1, much higher than that of thermally grown oxide, while their biaxial elastic modulus is only 4.6–5.1×1011 dyn/cm2. The stress in such films was found to increase when the films were exposed to a dry ambient or vacuum. The time constant for this change was found to be several minutes at room temperature.
Supernatural Inflation

Most models of inflation have small parameters, either to guarantee sufficient inflation or the correct magnitude of the density perturbations. In this paper we show that, in supersymmetric theories with weak scale supersymmetry breaking, one can construct viable inflationary models in which the requisite parameters appear naturally in the form of the ratio of mass scales that are already present in the theory. Successful inflationary models can be constructed from the flat-direction fields of a renormalizable supersymmetric potential, and such models can be realized even in the context of a simple GUT extension of the MSSM. We evade naive ``naturalness"arguments by allowing for more than one field to be relevant to inflation, as in ``hybrid inflation"models, and we argue that this is the most natural possibility if inflaton fields are to be associated with flat direction fields of a supersymmetric theory. Such models predict a very low Hubble constant during inflation, of order $10^3$-$10^4$ GeV, a scalar density perturbation index $n$ which is very close to or greater than unity, and negligible tensor perturbations. In addition, these models lead to a large spike in the density perturbation spectrum at short wavelengths.
Power-law singularities in string theory and M-theory

We extend the definition of the Szekeres–Iyer power-law singularities to supergravity, string and M-theory backgrounds, and find that are characterized by Kasner-type exponents. The near singularity geometries of brane and some intersecting brane backgrounds are investigated and the exponents are computed. The Penrose limits of some of these power-law singularities have profiles A ~ u−γ for γ ≥ 2. We find the range of the exponents for which γ = 2 and the frequency squares are bounded by 1/4. We propose some qualitative tests for deciding whether a null or timelike spacetime singularity can be resolved within string theory and M-theory based on the near singularity geometry and its Penrose limits.
Infrared spectroscopy of thin layers under ultra-high vacuum conditions

We summarize recent results from in-situ infrared spectroscopic studies of nanofilm growth. These studies, performed under ultra-high vacuum conditions with sub-monolayer sensitivity, exploited the relationship between morphology and structure on the one side and, on the other side, vibrational excitations and plasmonic ones. The studies were performed within various projects ranging from astronomy and high-energy physics to organic electronics and plasmonics. The results represent examples the description of which needs theoretical models beyond the use of Fresnel's formulae, the assumption of abrupt interfaces, and the use optical databases for bulk materials. For example, at the SiO-Si interface Si- O-Si bridges with Si-O bonds longer than in the bulk are formed which can be identified via their special vibration signals at unusually low vibration frequencies. From a thickness of about 1 nm on, the infrared spectra show typical SiObulk features. The lowered vibrational frequencies are attributed to changes in the average distribution of Si-O bond length close to the interface. On the diamond (100) surface, during Cr deposition, we observed the formation of a conducting nanocrystalline fcc phase of chromium. At a certain thickness, the nanocrystalline phase makes a phase transition to the typical bulk chromium phase. Cr is a preferred material for electric contacts in single-crystal diamond detectors the performance of which sensitively depends on the conductivity of the deposited Cr contact. On organic semiconductor layers metallization may be accompanied by an intermixing at the metal-semiconductor interface. Such intermixing can be observed as the appearance of new excitation features.
Major feedback factors and effects of the cloud cover and the relative humidity on the climate

In this paper we derive a new formula for the global temperature change and major feedback portions in the climate response. In our earlier paper we calculated from the experimental values the sensitivity about ${\rm 0.058~K/(W/m^2)}$. This means the negative feedback which reduced the sensitivity by factor $2.13$. In this paper we explain and derive the major portions in the feedback coefficient using the observed energy budget at the top of the climate and on the surface of the earth. The results also support strongly our earlier results of the low climate sensitivity ($\Delta T_{\rm 2CO_2}\approx 0.24^{\circ}$C). The major portions in the negative feedback coefficient in shortwave insolation are roughly clouds $63\%$, evaporation cooling $28\%$, and water vapour $9\%$. The new sensitivity is ${\rm 0.0605~K/(W/m^2)}$ which is reduced by factor $2.00$. The changes in cloud cover or in the relative humidity explain almost all the global temperature changes. The result is confirmed with experimental observations. On the other hand, the sun and the change in the vegetation are probably controlling most of the changes in cloudiness and humidity.
Multiple protostellar systems: I. A deep near infrared survey of Taurus and Ophiuchus protostellar objects

We performed a deep infrared imaging survey of 63 embedded young stellar objects (YSOs) located in the Taurus and Ophiuchus clouds to search for companions. The sample includes Class I and flat infrared spectrum protostellar objects. We find 17 companions physically bound to 15 YSOs with angular separations in the range 0.8–10´´ (110–1400 AU) and derive a companion star fraction of 23 ± 9% and 29 ± 7% for embedded YSOs in Taurus and Ophiuchus, respectively, about twice as large as that found among G dwarfs in the solar neighborhood. Therefore, binary and multiple protostellar systems are a very frequent outcome of the fragmentation of prestellar cores. In spite of different properties of the clouds and especially of the prestellar cores, the fraction of wide companions, 27 ± 6% for the combined sample, is identical in the two star-forming regions. This suggests that the frequency and properties of wide multiple protostellar systems are not very sensitive to specific initial conditions. Comparing the companion star fraction of the youngest YSOs still surrounded by extended envelopes to that of more evolved YSOs, we find evidence for a possible evolution of the fraction of wide multiple systems, which seems to decrease by a factor of about two on a timescale of ~10 5 yr. For the first time it is possible to confront the result of a multiplicity survey of a nearly complete population of embedded YSOs at an age of ~10 5 yr to numerical simulations of molecular cloud collapse which, after a few free fall times, reach this evolutionary stage. Somewhat contrary to model predictions, we do not find evidence for a sub-clustering of embedded sources at this stage on a scale of a few 100 AU that could be related to the formation of small- N protostellar clusters. Possible interpretations of this discrepancy are discussed.
The Space Telescope Imaging Spectrograph Design

The Space Telescope Imaging Spectrograph (STIS) instrument was installed on the Hubble Space Telescope (HST) during the second servicing mission, in 1997 February. Four bands cover the wavelength range of 115–1000 nm, with spectral resolving powers between 26 and 200,000. Camera modes are used for target acquisition and deep imaging. Correction for HST's spherical aberration and astigmatism is included. The 115–170 nm range is covered by a CsI MAMA (Multianode Microchannel Array) detector and the 165–310 nm range by a Cs2Te MAMA, each with a format of 2048 × 2048 pixels, while the 305–555 and 550–1000 nm ranges are covered by a single CCD with a format of 1024 × 1024 pixels. The multiplexing advantage of using these two‐dimensional detectors compared with the 1 × 512 pixel detectors of the first‐generation spectrographs is 1 or 2 orders of magnitude, depending on the mode used. The relationship between the scientific goals and the instrument specifications and design is discussed.