Sawtooth Shape Research Articles

Influence of Gaussian and Saw-tooth pulses in modulating excitation kinetics of impurity doped quantum dots

We explore the excitation kinetics in a single electron generic quantum dot theoretically. The quantum dot is doped with a repulsive impurity and subject to a pulsed field of Gaussian and saw-tooth pulse shapes that induce the excitation. The impurity potential has been assumed to have a Gaussian nature. The investigation reveals the sensitivity of the typical shape of the pulse, alongside the influences of dopant location, number of pulse, and some other characteristic pulse parameters towards modulating the excitation rate. Specifically, the other characteristic pulse parameters involve the width of the Gaussian pulse and the height of the saw-tooth pulse. In all the cases the typical pulse shapes announce its role on excitation kinetics unhesitatingly through a number of observations. The present study has also indicated enough evidence of twist in the mutual dominance of several factors that could favor and impede excitation accompanying the shift of dopant location. Importantly, those factors also depend severely on the pulse shape. The pulse shape and its characteristic parameters interfere delicately with the interplay between impurity location and number of pulses fed into the system and emerge as an important ingredient that can engineer the excitation kinetics.

Modeling of the Eurasian beaver (Castor fiber L.) population dynamics in the basin of a small Oka River tributary, the Tadenka River (Prioksko-Terrasnyi Nature Reserve)

A parametric time-discrete model for the beaver population dynamics starting from their invasion (1948) to the present day (2011) in the Tadenka River basin is described. It is shown that the population size tends to a stationary state in the presence of a quasi-periodic component of 14–26 years. Model estimates for the dynamics suggest that the periodic component has a sawtooth shape with the number of beavers increasing from minimum to maximum in each period for 6 years and decreasing from maximum to minimum during the remaining part of the period. The oscillation amplitude of the quasi-periodic component is approximately six individuals and displays a weak trend of increase. It is assumed that further development of this beaver population will depend on many random events influencing the factors that control beaver population size, such as specific geomorphological features of the area, restoration rate of food resources in the abandoned habitats, scale of beaver settlement development, and its rate. Stability analysis of the stationary solution and assessment of the model adequacy suggest that the proposed discrete model is appropriate for quantitatively describing the dynamics of the local beaver populations in other areas depending on the availability of food resources.

THIN STRUCTURE OF β-STABILITY LINE AND SYMMETRY ENERGY

We suggest a particular procedure of derivation of the beta-stability line, the nuclear Coulomb energy and the isotopic symmetry energy. The approach is based on the analysis of the A-dependency of the shift of neutron–proton chemical potentials Δλ = λn-λp. We observe the nonmonotonic (sawtooth) shape of the β-stability line as a function of mass number A and establish the relation of local maxima of the β-stability line to the mass numbers of the double-closed shells. The behavior of the symmetry energy coefficient b sym (A) at fixed neutron excess Y = N-Z is analyzed. We show that, qualitatively, b sym (A) has canyon-like behavior for a given value of Y. The width and the position of the bottom of such "canyon" depend on neutron excess.

Modelling the effects of dispersal mechanisms and hydrodynamic regimes upon the structure of microbial communities within fluvial biofilms

The spatial distribution of microbial taxa is determined primarily by physical and chemical environments and by dispersal. In a homogeneous landscape with limited dispersal, the similarity in abundance of taxa in samples declines with separation distance. We present a one-dimensional model for the spatial autocorrelation in abundances arising from immigration from some remote community and dispersal between environmentally similar landscape patches. Spatial correlation in taxa abundances were calculated from biofilms from the beds of two flumes which differed only in their bedform profiles; one flat and the other a periodic sawtooth shape. The hydraulic regime is approximately uniform over the flat bed, whereas the sawtooth induces fast flow over the peaks and recirculation in the troughs. On the flat bed, the correlation decline between samples was reproduced by a model using one biologically reasonable parameter. A decline was apparent in the other flume; however, a better fit was achieved when dispersal was not assumed constant everywhere. However, analysis of finer-resolution data for the heterogeneous flume suggested even this model did not adequately capture the community's complexity. We conclude that hydrodynamics are a strong driver of taxa-abundance patterns in stream biofilms. However, local adaptability must also be considered to build up a complete mechanistic model.

On the dynamic behavior of the anode–arc–root at the nozzle surface in a non-transferred plasma torch

The dynamic behavior of the anode–arc–root at the nozzle surface of a plasma torch was experimentally investigated in this work. A gas (N2) vortex–stabilized non-transferred arc torch with a thoriated tungsten rod (2wt %) cathode (3.2 mm diameter) and a coaxial anode (5 mm diameter, 30 mm length) was used in the experiment. By using a sweeping Langmuir probe in floating condition, the voltage of the plasma jet outside the nozzle was inferred. Arc voltage waveforms were also obtained. Data have been obtained for an arc current of 100 A and a gas flow rate of 30 Nl min−1. A typical sawtooth shape (i.e., restrike mode) (with a fluctuating level of ≈ ± 25 %) and a dominant frequency of ≈ 6.5 kHz was observed in the arc voltage waveforms, which is attributed to anode–arc–root movements along the anode surface followed by a restrike at a certain point close to the cathode. By performing a time correlation between the probe and arc voltage oscillograms together with simple estimations, the amplitude of the movement of the arc–root along the anode surface as well its velocity were inferred.

Free-stream velocity descriptions under waves with skewness and asymmetry

In shallow water, when waves shoal their orbital velocities exhibit skewness (velocity skewness) and asymmetry (acceleration skewness) in response to corresponding changes in the free surface. Near the bed, changes in the skewness and asymmetry of the time-varying velocities have important consequences for the residual velocities ‘spun up’ by the bottom friction and for sediment transport. In the wave boundary layer, where the largest sediment transport often occurs, there is a need to represent the free-stream velocity (the orbital velocity at the edge of the wave boundary layer) in a systematic way such that it can be mimicked in wave tunnel experiments and wave boundary layer models which usually do not represent the free surface. Since there is no readily accessible dynamical theory for shoaling waves that includes both skewness and asymmetry, it is necessary to synthesize the shoaling effect in a free-stream velocity description that is general enough to fit observed velocity time series. This paper reviews previous free-stream velocity descriptions, including the description of Abreu et al. (2010), and introduces a new description based on generalising a sawtooth wave shape. The paper quantifies all the relevant measures of skewness and asymmetry for each description. It then demonstrates that Abreu et al.'s (2010) description represents the most general one and improves upon their fitting techniques to observed free-stream velocities to further simplify it. When this description is used in conjunction with a characterisation of the velocity for irregular waves, such as that of Elfrink et al. (2006), it is possible to relate velocity skewness and asymmetry directly to the non-dimensional wave and beach parameters (wave height, surface wavelength and surf similarity parameter as a proxy for beach slope). MATLAB scripts are provided for the improved description of Abreu et al. (2010) and Elfrink et al.'s (2006) characterisation.

MICROSTRUCTURES AND PROPERTIES OF PULSED MIG ARC BRAZED-FUSION WELDED JOINT OF Al ALLOY AND GALVANIZED STEEL

Because there are great differences in physicochemical properties and mechanical properties between Al alloy and steel, their joining with high quality and high efficiency is one of difficult problems in study of welding technology. According to their difference in melting point, the brazing-fusion welding technology of Al alloy to steel was developed based on MIG welding. In pulsed MIG arc brazing-fusion welding process, the molten filler metal and Al alloy base metal will form the fusion welded joint, and will form the brazed joint together with unmelted steel plate, which can efficiently prevent the intermetallic compounds (IMCs) from the formation. With the digital pulsed MIG arc welding machine, the brazing-fusion welding of 6013-T4 Al alloy plate to galvanized steel plate was realized with the filler metal of ER4043, and the effect of welding heat input on microstructures and properties of the joint was studied. The results showed that there is a zinc-rich zone in the weld toe of fusion weld in the brazed-fusion welded joint, which is composed of Zn-Al eutectic, Al-rich � solid solutions and Fe3Al. Fe-Al IMCs layer on the brazed interface is 1.05—4.50 µm in thickness and become thicker with the welding heat input being increased. Fe-Al IMCs with sawtooth or tongue shape grow towards the weld, which mainly includes FeAl2, Fe2Al5 and Fe4Al13. With the welding heat input

Mechanical Stability of the Cardiac Myosin Binding Protein-C (CMybP-C) Motif is Phosphorylation-Dependent

Enhanced cardiac contractility results from phosphorylation within the cMyBP-C motif domain by affecting the interaction of cMyBP-C's N-terminus with actin and/or myosin. We investigated whether motif (i.e. C1C2 linker) phosphorylation alters its structural conformation by characterizing the force-extension behavior of expressed N-terminal cMyBP-C fragments (i.e.C0C3) that contain the motif using atomic force spectroscopy. Proteins were adsorbed onto glass slides, bound non-specifically to SiNi AFM probes, and stretched at 700nm/s. Force-extension traces showed the characteristic sawtooth shape of unfolding immunoglobulin domains, and were well fitted by the wormlike chain model. The model fits produced a median persistence length of 0.36nm and an average C0C3 contour length of 71.5nm, suggesting that the motif is disordered and freely extensible when unphosphorylated. PKA phosphorylation did not change immunoglobulin unfolding force or persistence length but decreased the contour length by 27nm, suggesting that the motif assumed a folded configuration that is stable under load. This was investigated further by varying the extent of phosphorylation using phosphomimetic mutants, in which serines 273, 282, and 302 were replaced with different combinations of alanines or aspartic acids in order to mimic the unphosphorylated and phosphorylated states respectively. While substitution with all alanines or all aspartic acids produced similar results to the control and PKA treated fragments respectively, phosphorylation at only one or two sites did not reduce contour length significantly. This implies that phosphorylation at all three sites is required for motif folding to be stable under load, while partial phosphorylation may result in a fold which is readily extended at low force. In conclusion, cMyBP-C phosphorylation could modulate the cMyBP-C's N-terminal domain interactions with actin and/or myosin by folding the motif in such a way that binding sites for actin and/or myosin are hidden.

Marina di Cecina Urban Beach: a Shore Protection Project

AMINTI, P.L., BARTOLETTI, E., BERRIOLO, G., BINI, A., BONINSEGNI, G., MORI, E., PRANZINI, E and VANNUCCHI, V., 2011. Marina Di Cecina Urban Beach: a Shore Protection Project. In: Micallef, A. (ed.), MCRR3-2010 Conference Proceedings, Journal of Coastal Research, Special Issue, No. 61, pp. 282–289. Grosseto, Tuscany, Italy, ISSN 0749-0208.Marina di Cecina is a tourist town built on the southern side of Cecina river mouth. Its urban beach has been undergoing severe erosion since the early 20th century as a consequence of reduced river sediment input. Some groins were constructed after the collapse of the first line of houses near the waterline. Immediately the shoreline assumed a characteristic saw-tooth shape and beach use and recreational facilities had to adapt to this uneven sand distribution. In 1990 two of the three main groins were extended with submerged segments and limited artificial nourishment was also performed. Some discontinuous submerged detached breakwaters were added later within the groin field, which resulted in sediment dispersion offshore. The beach was maintained with occasional nourishment, but its width could not support profitable recreational activities and some tourism facilities are still being damaged today by waves during severe storms. To solve these problems, the Livorno Province administration within the Regional shore protection plan, has performed a rehabilitation project at this urban beach. The project is based on the reconfiguration of the whole defence system, removing parallel structures and modifying the groin field; varying the lengths to reach a new alignment of the tips, in order to stabilise a new and more uniform beach to be obtained by means of artificial nourishment. Groin tips will be asymmetric, to reduce wave reflection on the exposed side; some of them will be extended with a long submerged segment made with T-shape concrete precast elements. Groins will be constructed using large flat-faced stones in order to obtain regular slopes, whereas a central pathway made of concrete will allow easy access to pedestrians. Moreover, at the extremities of the field, where parking facilities are present, groins will end with a mildly sloped ramp to give wheelchair users access to the sea.

Effect of cutting speed on surface integrity and chip morphology in high-speed machining of PM nickel-based superalloy FGH95

High-speed machining is being recognized as one of the key manufacturing technologies for getting higher productivity and better surface integrity. FGH95 powder metallurgy superalloy is a kind of nickel-based superalloy which is produced by near-net-shape technology. With increasing demands for high precision and high performance of FGH95 components in aerospace industry, it is essential to recognize that the machined surface integrity may determine machined part service performance and reliability. Then, little is known about the machined surface integrity of this superalloy. Thus, the surface integrity in high-speed machining of FGH95 is investigated in this paper. Experiments are conducted on a CNC milling center with coated carbide tools under dry cutting conditions. The surface integrity is evaluated in terms of surface roughness, microhardness, and white layer. The influence of cutting speed on chip morphology is also investigated. Experiment results show that surface integrity and chip morphology of FGH95 are very sensitive to the cutting speed. When cutting speeds are below 2,400 m/min, the values of surface roughness have little variation, while when cutting speeds are in the range of 2,800–3,600 m/min, the values of surface roughness are higher than that of other cutting speeds. Severe work hardening is observed resulting from high-speed machining of FGH95 superalloy. The higher the cutting speed, the higher the surface hardness. When cutting speeds are in the range of 2,800–3,600 m/min, the white layer thickness is slightly higher than that of other cutting speeds. In high-speed machining of FGH95, the chip is segmented and has a typical sawtooth shape. The degree of serrated chip increases with the cutting speed. When the cutting speeds exceed 2,400 m/min, serrated chips change into fragment chips.

Study of flow induced by sine wave and saw tooth plasma actuators

The effect of plasma actuator that uses saw-tooth or sine-wave shape electrodes on boundary layer flows is experimentally investigated. The measurement results are compared with a corresponding standard configuration (conventional design using two rectangular strip electrodes)—the actuator that produces a nearly two-dimensional horizontal wall jet upon actuation. PIV measurements are used to characterize the actuators in a quiescent chamber. Operating in a steady manner, the new actuators result in the formation of streamwise and spanwise vortices. That is to say, the new actuators render the plasma actuators inducing three-dimensional variations in the shear layer, offering significant flexibility in flow control. The affected flowfield with the new actuators is significantly larger than that with the conventional linear actuators. While the conventional linear actuators affect primarily the boundary layer flow on a scale of about 1 cm above the wall, the new actuators affect the near wall region at a significantly larger scale. This new design broadens the applicability and enhances the flow control effects and it is potentially a more efficient flow control device.

Multiharmonic fields driven adiabatic quantum pumps in nanowire structures

A dc current can be pumped through a nanostructure by two out-of-phase ac driving fields. In this approach, we investigate the pumped current properties driven by multiharmonic ac fields in nanowire structures. Considering the first five harmonics, the adiabatically pumping properties driven by approximate square, sawtooth, and triangle-shape ac waves are discussed. It is found that the pumped current varies with the phase difference in a square and sawtooth shape, respectively, under corresponding driven fields. Sinusoidal relation governs in the pump driven by a triangle-shape ac field.

Vertically arrayed Ga-doped ZnO nanorods grown by magnetron sputtering: The effect of Ga contents and microstructural evaluation

Vertically aligned Ga-doped ZnO (ZnO:Ga) nanorods were grown on sapphire substrates without buffer layers under conditions designed to ensure rapid growth rates with a magnetron sputtering system. Unlike the undoped ZnO layer with microsize protrusions, the 1 and 2 wt% Ga doping induced the formation of uniform nanorod arrays with epitaxial growth behavior. In the initial growth stage, the ZnO:Ga layers exhibited island growth with pyramidal shapes due to enhanced misfit strain. This promoted preferential growth along the c-axis, resulting in the formation of nanorod arrays ,without buffer layers. However, the increased stress stored in the ZnO:Ga layers generated high density of stacking faults, which led to an intense donor–acceptor pair emission at 3.31 eV. In addition, the sample doped with a high Ga amount (2 wt%) had rotated crystal phases, resulting in rough sidewalls with nano-branch or sawtooth shapes.

Theoretical study on hydrophilicity and thermodynamic properties of polyfluorinated dibenzofurans

Logarithm values of octanol–water partition coefficients (log K ow) of polyfluorinated dibenzofurans (PFDFs) were calculated based on group contributions, and their thermodynamic properties in the ideal gas state at 298.15 K and 1.013 × 10 5 Pa were calculated using a combination of quantum mechanical computations performed with the Gaussian 03 program at the B3LYP/6-311G * level. The isodesmic reactions were designed to calculate standard enthalpy of formation ( Δ H f θ ) and standard free energy of formation ( Δ G f θ ) of PFDF congeners. By establishing relationships between these properties (including log K ow, standard state entropy S θ, Δ H f θ , Δ G f θ ) and the number and position of fluorine atom substituents ( N PFS), it was found that the fluorine substitution pattern strongly influences all of these properties of the compounds. The relation curve of log K ow values varying with the fluorine substitution pattern presented a three-level sawtooth shape. Intramolecular repulsive forces exist between an oxygen-adjacent fluorine atom on phenyl ring and the oxygen of dibenzofuran, between ortho-substituted fluorine atoms on a phenyl ring, and between two adjacent fluorine atoms on different phenyl rings. Their repulsion energies were ascertained by comparing Δ G f θ values to be approximately 14 kJ mol −1–17 kJ mol −1, 18 kJ mol −1–22 kJ mol −1 and 7 kJ mol −1–9 kJ mol −1, respectively. According to the relative magnitude of their Δ G f θ , the relative stability order of PFDF congeners was theoretically proposed.

A Visible Sawtooth

Radio frequency (RF) generators can be programmed to emit many differently shaped oscillatory patterns, from sinusoidal waves associated with single frequencies to square and sawtooth shapes that emerge when frequencies spanning multiple octaves are mixed. Analogous manipulation of optical fields is rather more challenging, because laser sources cannot usually produce many mutually coherent components spaced octaves apart. Chan et al. (p. [1165][1], published online 20 January; see the Perspective by [Yavuz][2] ) have now succeeded in preparing optical sawtooth and square wave pulses by assembling discrete combs of five harmonics, from the blue to the mid-infrared, derived through Raman shifting in a hydrogen cell and demonstrate a method for characterizing such waveforms based on linear cross-correlation. [1]: /lookup/doi/10.1126/science.1198397 [2]: /lookup/doi/10.1126/science.1203018

Column Shortening Analysis with Lumped Construction Sequences

An analysis method with lumped construction sequences for the column shortening of tall buildings is proposed and its efficiency is investigated. The lumped model shows results that are close to the exact model in post-installation shortening as well as total shortening. The saw-tooth shape of post-installation shortening can be modified by curve fitting and the modified shortenings show good agreement with the exact values. The effect of the size of the lumping is studied and about 1/15 of the total stories of the building is recommended considering the accuracy of the results and the reduction in computing time. The proposed method is expected to be used effectively at the design stage of a tall building when repetitive analysis is required.

Nonlinear stationary acoustic wave in a solid with dislocations

It is shown that a nonlinear stationary acoustic wave can be formed in a solid with dislocations. Such a wave is periodic and moves faster than acoustic signals in a linear medium. The wave has a saw-tooth shape and its wavelength increases with the amplitude.

The optimal elastic flagellum

Motile eukaryotic cells propel themselves in viscous fluids by passing waves of bending deformation down their flagella. An infinitely long flagellum achieves a hydrodynamically optimal low-Reynolds number locomotion when the angle between its local tangent and the swimming direction remains constant along its length. Optimal flagella therefore adopt the shape of a helix in three dimensions (smooth) and that of a sawtooth in two dimensions (nonsmooth). Physically, biological organisms (or engineered microswimmers) must expend internal energy in order to produce the waves of deformation responsible for the motion. Here we propose a physically motivated derivation of the optimal flagellum shape. We determine analytically and numerically the shape of the flagellar wave which leads to the fastest swimming for a given appropriately defined energetic expenditure. Our novel approach is to define an energy which includes not only the work against the surrounding fluid, but also (1) the energy stored elastically in the bending of the flagellum, (2) the energy stored elastically in the internal sliding of the polymeric filaments which are responsible for the generation of the bending waves (microtubules), and (3) the viscous dissipation due to the presence of an internal fluid. This approach regularizes the optimal sawtooth shape for two-dimensional deformation at the expense of a small loss in hydrodynamic efficiency. The optimal waveforms of finite-size flagella are shown to depend on a competition between rotational motions and bending costs, and we observe a surprising bias toward half-integer wave numbers. Their final hydrodynamic efficiencies are above 6%, significantly larger than those of swimming cells, therefore indicating available room for further biological tuning.

Topological Insulator Nanowires and Nanoribbons

Recent theoretical calculations and photoemission spectroscopy measurements on the bulk Bi(2)Se(3) material show that it is a three-dimensional topological insulator possessing conductive surface states with nondegenerate spins, attractive for dissipationless electronics and spintronics applications. Nanoscale topological insulator materials have a large surface-to-volume ratio that can manifest the conductive surface states and are promising candidates for devices. Here we report the synthesis and characterization of high quality single crystalline Bi(2)Se(3) nanomaterials with a variety of morphologies. The synthesis of Bi(2)Se(3) nanowires and nanoribbons employs Au-catalyzed vapor-liquid-solid (VLS) mechanism. Nanowires, which exhibit rough surfaces, are formed by stacking nanoplatelets along the axial direction of the wires. Nanoribbons are grown along [1120] direction with a rectangular cross-section and have diverse morphologies, including quasi-one-dimensional, sheetlike, zigzag and sawtooth shapes. Scanning tunneling microscopy (STM) studies on nanoribbons show atomically smooth surfaces with approximately 1 nm step edges, indicating single Se-Bi-Se-Bi-Se quintuple layers. STM measurements reveal a honeycomb atomic lattice, suggesting that the STM tip couples not only to the top Se atomic layer, but also to the Bi atomic layer underneath, which opens up the possibility to investigate the contribution of different atomic orbitals to the topological surface states. Transport measurements of a single nanoribbon device (four terminal resistance and Hall resistance) show great promise for nanoribbons as candidates to study topological surface states.

Poncelet's porism in the finite real plane

In this article, we continue exploring Poncelet's curves, leveraging their connection to the numerical ranges of special matrices. This connection was recently discovered by (H.-L. Gau and P.Y. Wu, Numerical range of S(ϕ), Lin. Multilin. Alg. 45 (1998), pp. 49–73) and (B. Mirman, Numerical ranges and Poncelet curves, Lin. Alg. Appl. 281 (1998), pp. 59–85). Main result: separated Poncelet's curves may be generated by alternating (in sign) functions and matrices of a special structure. Poncelet's polygons for separated Poncelet's curves have a typically saw-tooth shape.