Miracle-dz/UniFAR-FTUs huggingface dataset:
Form and wave drag due to stably stratified turbulent flow over low ridges

We investigate how stable stratification affects the aerodynamic force, or form drag, induced by turbulent boundary-layer flow over two-dimensional hills. Both analytical and numerical models are used to calculate the flow and thence the form drag on the hill. In the analytical model we use a two-layer, truncated mixing-length, turbulence model, which is consistent with scaling arguments and which produces reliable estimates of the form drag for the neutral flow. The form drag is also calculated analytically using an eddy-viscosity model, and the results compare well with values computed with the nonlinear numerical model that uses a similar turbulence model. The leading-order contribution to the form drag is from a non-separated sheltering mechanism, which is similar to the mechanism in neutral flow. Stable stratification changes the magnitude of this mechanism through several effects. For weak stratification the predominant effect is an increase in shear in the upstream wind profile across a middle layer, which increases the form drag by a factor of two or more. There is indirect experimental evidence to support this finding. If the stratification is more stable, then the shear across the middle layer becomes limited because the boundary layer has a finite depth. Then the dynamical effect of buoyancy on the pressure perturbation becomes important and reduces the form drag, eventually to zero. For still more stable stratification, gravity waves and associated wave drag are produced. The analysis shows that the appropriate scaling velocity for wave drag is the approach-flow wind speed evaluated at the middle-layer height. The relationship between the form and wave drag components is investigated by evaluating the analytical formula for the drag on isolated hills of two idealized shapes. For weak stratification the form drag dominates, but as the stratification becomes more stable the wave drag increases and first equals the form drag, at a value that depends on the hill shape, and then dominates.
The coupling between scales in shear flows

In order to explore the relationship between the large‐ and small‐scale motions in turbulent shear flows, a number of flows have been studied based on short‐time correlation measurements. The shear flows investigated are boundary layers, plane and axisymmetric mixing layers, plane wakes and the far fields of plane and circular jets. The coupling between the scales has been obtained by correlating the low‐frequency component of the u‐velocity signal with a signal that is similar to the envelope of the high‐frequency part of the velocity signal. The coupling is found to be significant in all flows. Phase reversal across the shear region is found to occur in the boundary layers and the mixing layers only. This is interpreted to mean that in boundary layers and mixing layers, the streamwise extent of the large structure over which the small‐scale activity reaches a peak moves at one transverse end of the large structure over which its ensemble averaged u fluctuation is positive to another where it is negative. This phase shift (≂180°) of the location of the peak activity of the small scales with respect to the large structure takes place gradually resulting in a midlayer where the phase difference is about 90°. On the other hand, in the far field of the jets and wakes, all across the layer, the peak activity of the small scales always remains confined to that half of the streamwise extent of the large structure where its ensemble averaged u fluctuation is positive; in the remaining streamwise half of the large structure, the small scales remain dormant.
On the Metal–Insulator Transitions in VO2 and Ti2O3 from a Unified Viewpoint

The metal–insulator (M–I) transitions in VO 2 and Ti 2 O 3 were investigated using the three-band Hubbard model in connection with the on-site exchange interaction and lattice distortions. Although these two compounds have different crystal structures, the mechanism of the phase transitions can be understood from a unified viewpoint; an increase in energy level separation among the t 2 g orbitals caused by the lattice distortion triggers an abrupt change in the electron configuration in doubly occupied sites from an S =1 Hund's coupling state to a low-spin S =0 state with much larger energy and this strongly suppresses the charge fluctuation, resulting in localization of electrons. These M–I transitions are not induced by an increase in relative strength of the Coulomb interaction against the electron hopping as in the conventional scenario of the Mott–Hubbard transition but by the level splitting among the t 2 g orbitals against the on-site exchange interaction. Switching of the nearest-neighbor spin and.
Velocity measurements in turbulent gaseous mixtures induced by Richtmyer–Meshkov instability

Instantaneous velocity measurements in a gaseous mixture arising from the shock wave-induced Richtmyer–Meshkov instability are conducted for the first time in a shock tube. Laser Doppler anemometry gives us the evolution of the axial velocity fluctuations of the mixing zone, before and after its interactions with reflected shock waves from the shock tube end wall. Experimental results demonstrate that a turbulent mixing zone is generated by the incident shock wave. Afterwards, the axial variance decreases before being amplified by the first reshock interaction through a baroclinic effect. Before the second reshock arrival, we measure once again a decrease of the turbulence level which is explained by both diffusion and dissipation.
Thermal bifurcation in the solar outer atmosphere

Two distinct plasma thermal states are possible in the solar outer atmosphere, owing to the bifurcated character of the low-temperature cooling function at small optical depths. In radiative equilibrium, the plasma is strongly cooled to temperatures well below 4000 K by surface emission in the . delta.V = 1 fundamental vibration-rotation bands of carbon monoxide. However, when significant mechanical energy deposition is present in addition to the radiative heating component, the only effective cooling channel available to stabilize the plasma is optically thin emission in the recombination continuum of H/sup -/. As a result, thermal equilibrium in a mechanically heated atmospheric zone can be attained only for temperatures above T/sub crit/roughly-equal4900 K because H/sup -/ is itself a net radiative heating agent for temperature cooler than T/sub crit/. Thermal bifurcation effects in the solar outer atmosphere are encouraged by the likelihood that mechanical energy deposition is significantly enhanced in small-scale, discrete structures, namely, magnetic flux tubes.
Feasibility of Guided Entry for a Crewed Lifting Body Without Angle-of-Attack Control

The feasibility of flying a crewed lifting body, such as the HL-20, during entry from low Earth orbit without the steady-state body flap deflections required for angle-of-attack control was evaluated. This entry strategy mitigates the severity of the aerothermal environment on the vehicle’s body flaps and reserves control power for transient steering maneuvers. A real-time numeric predictor–corrector entry guidance algorithm was developed to accommodate the range of vehicle trim angle-of-attack profiles possible in the absence of angle-of-attack control. Results show that it is feasible to steer the vehicle from low Earth orbit to a desired target with real-time guidance while satisfying a reasonable suite of trajectory constraints, including limits on peak heat rate, peak sensed deceleration, and integrated heat load. Uncertainty analyses confirm this result and show that the vehicle maintains significant performance robustness to expected day-of-flight uncertainties. Additionally, parametric scans over .
3D flow field in a scour hole at a wing-wall abutment

Experiment was conducted in a laboratory flume to measure the 3D turbulent flow field by an acoustic Doppler velocimeter in a scour hole at a 45? wing-wall abutment under a clear water regime. The profiles of time-averaged velocity components, turbulence intensity components, turbulent kinetic energy and Reynolds stresses at different azimuthal planes are presented. In the upstream, vector plots of flow field at azimuthal and horizontal planes show the presence of a large primary vortex associated with a downflow within the scour hole. In the downstream, the flow is upward. The bed shear stresses within the scour hole are estimated from the Reynolds stresses and the velocity gradients. The data presented in this study would be useful to the researchers for the future development and validation of theoretical models of flow field in a scour hole at bridge abutments
Type Ia supernovae in late type galaxies : reddening correction, scale height, and absolute maximum magnitude

We have collected and analyzed the color excess data for the best photometrically studied type Ia supernovae (SN Ia) which occurred in late type galaxies. From these data, a ratio of the B band to selective extinction in the parent galaxies of A B /E(B-V) = 3.35 ± 0.25 (1 σ) is found. This indicates that the extinction curves in late type galaxies have similar properties to that of our Galaxy. A new calibration for the absolute magnitude at maximum of SN Ia in late type galaxies = -19.24 ± 0.18 (1 σ) + 5 log(H 0 /75) is obtained, which is marginally brighter than the recent determinations for type Ia supernovae observed in elliptical (dust-free) galaxies, and appears to confirm the potential of SN Ia as standard candles for distance determinations
A Three-Dimensional View of the Evolution of Midlatitude Stratospheric Intrusions

Abstract Three-dimensional views of midlatitude stratospheric intrusions are presented. The views are obtained by plotting a surface of constant potential vorticity (PV), where the PV is diagnosed from a 6-day run of the U.K. Universities Global Atmospheric Modelling Project General Circulation Model. The PV = 1 × 10−6 K kg−1 m2 s−1 (=1 PVU) isosurface is chosen as representative of the tropopause. The evolution of this surface is examined during the development of baroclinic waves in the Northern Hemisphere during October 1990. The developments show a number of features expected during the evolution of upper-level troughs, such as vortex roll-up, and the generation of tropopause folds, in which air from the stratosphere intrudes downward into the troposphere. However, it is shown that the combined effects of deformation and convergence lead to the rapid collapse of folded features to leave low-level tubes of PV, together with higher-level filaments. The result is that the air intruded in the vicinity of .
Magnetic Reconnection Coupled with Heat Conduction

Magnetic reconnection coupled with nonlinear anisotropic heat conduction is studied by using a two-dimensional magnetohydrodynamic (MHD) simulation. Owing to the heat conduction effect, the adiabatic slow-mode MHD shocks that emanate from the neutral point are dissociated into conduction fronts and isothermal shocks. The dependence on heat conductivity of the physical variables in the outflow region, such as temperature, density, and velocity, are studied. We also discuss the energy release and the reconnection rate.
Linear-mode photon counting with the noiseless gain HgCdTe e-APD

A linear mode photon counting FPA using HgCdTe MWIR cutoff e-APDs has been designed, fabricated, and characterized. The broad spectral range (0.4 μm to 4.3 μm) is unique among photon counters, making this a "first of its kind" system spanning the visible to the MWIR. The low excess noise ((F(M) ≈ 1) of the e-APDs allows for robust photon detection while operating at a stable linear avalanche gain in the range of 500 to 1000. The ROIC design included a very high gain-bandwidth product RTIA (3x1011 Ohm-Hz) and a 4 ns output digital pulse width comparator. The ROIC had 16 high bandwidth analog and 16 LVDS digital outputs. The 2x8 array was integrated into an LN2 Dewar with a custom LCC and daughter board design that preserved high bandwidth analog and digital signal integrity. The 2x8 e-APD arrays were fabricated on 4.3 μm cutoff HgCdTe and operated at 84 K. The measured dark currents were approximately 1 pA at 13 V bias where the measured APD gain was 500. This translates to a predicted dark current induced dark count rate of less than 20 KHz. Single photon detection was achieved with a photon pulse SNR of 13.7 above the amplifier noise floor. A photon detection efficiency of 50% was measured at a background limited false event rate (FER) of about 1 MHz. The measured jitter was in the range of 550 ps to 800 ps. The demonstrated minimum time between distinguishable events was less than 10 ns.
Laser beam spatial profile determination by pulsed photoacoustics: exact solution

The pulsed photoacoustic spectroscopy technique is one of the oldest but respectable techniques which offer some unique features that are relevant to trace gas monitoring. Despite obvious advantages there are some drawbacks that have so far alienated this spectroscopy technique from routine air monitoring. One of them is the additional instrumentation necessity to fulfill the requirement for an accurate knowledge of the spatial and temporal profiles of the excitation light source. Here we present one method for a laser beam spatial profile determination and simultaneous vibrational–translational relaxation time calculation. It is based on the temporal shape analysis of the photoacoustic signals. Symmetric laser beam spatial profiles are obtained with a high level of accuracy. Even though this method does not work in real time, it gives a good basis for future beam profile investigations. Experimental signals used in our analysis are obtained after infrared multiphoton absorption in the SF6–Ar mixture.
İlköğretim Beşinci Sınıf Öğrencilerinin Problem Kurma Becerilerinin İncelenmesi

Bu arastirmanin amaci ilkogretim besinci sinif ogrencilerinin problem kurma becerilerini, kullandiklari tekniklere gore incelemektir. Bu calismada nitel arastirma yaklasimi benimsenmistir. Calisma grubunu 20092010 egitim ogretim doneminde Konya ilinde bir ilkogretim okulunun 5. sinifinda ogrenim goren ogrenciler (n=20) olusturmustur. Calismada veri toplama araci olarak, Fidan (2008) tarafindan gelistirilen ve dort isleme dayali problemlerden olusan “Problem Cozme ve Kurma Etkinlik Kâgitlari” kullanilmistir. Arastirmaya katilan ogrencilere etkinlik kâgitlarinda yer alan problemler, Polya’nin belirttigi adimlara gore sinif ortaminda cozdurulmus ve daha sonra cozdukleri problemlerle ilgili problem kurmalari istenmistir. Ogrencilerin kurduklari problemler, Lave, Smith ve Butler’in (1989) belirttigi tekniklere gore incelenmistir. Elde edilen verilerin frekans ve yuzdeleri hesaplanmis, tablolar halinde sunulmustur. Arastirma sonuclarina gore, ogrencilerin cogunun problem kurarken kullandigi teknik, kosullari ve konuyu degistirmeyip verilen verilerin degerlerini degistirme yonundedir. “Verilen ve istenen bilgiyi ters cevirme” ve “verilen verileri ve konuyu degistirmeyip, kosullari degistirme” siniflandirmalarinda hicbir problemin yer almadigi belirlenmistir
Structural and optical properties of (Ag,Cu)(In,Ga)Se2 polycrystalline thin film alloys

The structural and optical properties of pentenary alloy (Ag,Cu)(In,Ga)Se2 polycrystalline thin films were characterized over the entire compositional range at a fixed (Cu + Ag)/(In + Ga) ratio. Films deposited at 550 °C on bare and molybdenum coated soda-lime glass by elemental co-evaporation in a single-stage process with constant incident fluxes exhibit single phase chalcopyrite structure, corresponding to 122 spacegroup (I-42d) over the entire compositional space. Unit cell refinement of the diffraction patterns show that increasing Ag substitution for Cu, the refined ao lattice constant, (Ag,Cu)-Se bond length, and anion displacement increase in accordance with the theoretical model proposed by Jaffe, Wei, and Zunger. However, the refined co lattice constant and (In,Ga)-Se bond length deviated from theoretical expectations for films with mid-range Ag and Ga compositions and are attributed to influences from crystallographic bond chain ordering or cation electronegativity. The optical band gap, derive.
On the interaction of a planar shock with a light polygonal interface

Abstract The interaction of a planar shock wave with a polygonal $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}{\mathrm{N}}_2$ volume surrounded by ${\mathrm{SF}}_6$ is investigated experimentally and numerically. Three polygonal interfaces (square, triangle and diamond) are formed by the soap film technique developed in our previous work, in which thin pins are introduced as angular vertexes to connect adjacent sides of polygonal soap films. The evolutions of the shock-accelerated polygonal interfaces are then visualized by a high-speed schlieren system. Wave systems and interface structures can be clearly identified in experimental schlieren images, and agree well with the numerical ones. Quantitatively, the movement of the distorted interface, and the length and height of the interface structures are further compared and good agreements are achieved between experimental and numerical results. It is found that the evolution of these polygonal interfaces is closely related to their initial shapes. In the square interface, two vortices are generated shortly after the shock impact around the left corner and dominate the flow field at late stages. In the triangular and diamond cases, the most remarkable feature is the small ‘ ${\mathrm{SF}}_6$ jet’ which grows constantly with time and penetrates the downstream boundary of the interface, forming two independent vortices. These distinct morphologies of the three polygonal interfaces also lead to the different behaviours of the interface features including the length and height. It is also found that the velocities of the vortex pair predicted from the theory of Rudinger and Somers (J. Fluid Mech., vol. 7, 1960, pp. 161–176) agree with the experimental ones, especially for the square case. Typical free precursor irregular refraction phenomena and the transitions among them are observed and analysed, which gives direct experimental evidence for wave patterns and their transitions at a slow/fast interface. The velocities of triple points and shocks are experimentally measured. It is found that the transmitted shock near the interface boundary has weakened into an evanescent wave.
Sufficient conditions for the existence of optimum beam patterns for unequally spaced linear arrays with an example

Dolph's method for determining the optimum element currents for half-wavelength equispaced discrete linear arrays is generalized to symmetric discrete linear arrays. The theorem proved gives sufficient conditions for the existence of optimum beam patterns for arrays with elements symmetrically positioned about the array center, but with fixed unequal spacings between the elements. The conditions are such that the Remes exchange algorithm for minimax approximation of functions can be employed to compute the optimum element currents corresponding to an optimum beam pattern directly from the given spacings of the elements. Half-wavelength spaced linear arrays satisfy the conditions of the theorem; therefore, it provides a new method of calculating the well-known Dolph-Chebyshev element currents. An example with unequal spacings is included to show the utility of the method even when the hypotheses of the theorem may not be met.
Secondaries of eclipsing binaries. VII: The spectroscopic triple and visual double V505 Sagittarii

High signal-to-noise ratio Reticon observations of this Algol system reveal the secondary's Na D lines. These observations and accompanying observations of the primary made in the blue provide the secondary velocity curve and a redetermination of the primary velocity curve. The semiamplitudes of the primary and secondary are 101.3±1.8 km s −1 and 195±5 km s −1 , respectively, and yield masses of 2.20±0.09 M⊙ and 1.15±0.05 M⊙, respectively
Activation energy and prefactor for surface electromigration and void drift in Cu interconnects

Surface electromigration rates on oxide-free surfaces of unpassivated damascene Cu interconnect segments have been determined through electromigration testing under vacuum. Electromigration-induced voids grew at the cathode end of the segments due to a flux divergence at refractory-metal-lined vias to the lead lines below the test segment. Copper diffusivity on a clean Cu surface was determined by measuring the size of the voids as a function of time and test temperature at a fixed current. An activation energy of 0.45±0.11eV and a prefactor of 3.35×10−12m2∕s were found for the product of the effective charge z* and the surface diffusivity Ds. This result is shown to be consistent with void drift rates measured in passivated interconnects.
Unsteady heat or mass transport from a suspended particle at low Péclet numbers

Unsteady heat or mass transport from a particle with an arbitrary shape suspended in a fluid of infinite expanse is considered in the limit of small Péclet numbers where diffusion is dominant. In a frame of reference in which the particle appears to be stationary, the velocity of the fluid is uniform or varies in a linear manner with respect to the spatial coordinates, with an arbitrary time dependence. The temperature or concentration of a species at the surface of the particle is held at a certain constant value, whereas that at infinity is held at another constant value. Two particular problems are considered, both to leading order with respect to the Péclet number: (a) the rate of transport from a particle that is introduced suddenly into a steady flow near the steady state; and (b) the average rate of transport from a particle that is suspended in a time-periodic flow. The theory uses the method of matched asymptotic expansions and employs the Green's function of the convection–diffusion equation for a generally unsteady uniform or linear flow. The Green's function is derived in closed form by first performing a transformation to a Lagrangian framework. In the first problem of transient transport, it is found that the functional form of the rate of transport near the steady state is affected strongly by the structure of the incident flow: the decay in uniform or elongational flow is exponential, whereas the decay in simple shear flow is algebraic. In the second problem of transport in a periodic flow, it is found that the value of a properly defined frequency parameter has a strong influence on the mean rate of transport, for all types of flow. The oscillation induces convective mixing and thereby reduces the mean rate of transport by a substantial factor. The ability of the theory to describe another situation of heat or mass transport considered by Pedley is also discussed.
On generalized spin-boson models with singular perturbations

In this paper we consider generalized spin-boson models with singular perturbations. It is proven that under the infrared regularity condition Hamiltonians have the unique ground state for suﬃciently small values of coupling constants. In addition it is shown that the asymptotic creation and annihilation operators of boson ﬁeld exist.
New Zero-stable Block Method for Direct Solution of Fourth Order Ordinary Differential Equations

A zero-stable block method for solving fourth order initial value problems of ordinary differential equations directly is proposed. Interpolation and collocation techniques are employed in developing the method. Power series approximate is used as a basis function where its fourth derivative is collocated at all the grid points within the specified interval. Furthermore, the properties of the method developed, that is, zero-stability, consistency, convergence, order and error constant are established. The new method performs better than the existing methods in terms of accuracy.