Aerodynamics Of Soccer Balls And Volleyballs

The purpose of this study was to investigate range, flight time, speed and trajectory of selected official soccer balls and volleyballs in a constant release angle (18 degree) shot by a ball gun with a hydraulic shooting steel leg mechanism in an indoor soccer hall. Five soccer balls (m=0.422 ± 0.010 kg, d=0.108 + 0.002 rn, p=(0.69 + 0.01) x 105 Nm-2) and five volleyballs (m=0.278 ± 0.006 kg, d=0.105 + 0.002 rn, p=(0.69 ±0.01) x 105 Nm-2) were used. Three speeds of the kicking steel leg were applied to the stationary and rotating balls with two constant angular velocities (45.6 and 65.0 radls). All shots of the balls were recorded with two JVC 707 5-VHS camcorders (50 Hz) for kinematic and kinetic motion analysis. An APAS performance analysis system was used for detailed 3D analysis of the release phase of the shot. The range of the ball was measured in x-z coordinates on the Astroturf ground. A Panasonic camcorder with timer was used to measure the flight time of the ball. A 3- way ANOVA was applied in order to study the differences of the balls and their behaviour in the placid air. The release velocities of the stationary soccer balls with three speed categories .were 18.8 + 0.1 ms·1, 23.1 ± 0.1 msand 26.5 ± 0.1 ms-1 and in volleyballs 20.5 ± 0.2 ms-I, 25.6 ± 0.2 ms-1 and 29.4 ± 0.2 ms-1, respectively. The range of the fastest shot off the soccer balls was on average 44.8 m with the lateral deviation of 3.3 degrees. The average range of the volleyballs in the fastest shots without spin was 45.2 m with the lateral deviation of 4.8 degrees. The average ground speeds in the fastest shots of the soccer ball and volleyball were 20.6 ms-1 and 24.7 ms-1, respectively. With the fastest spin and shot the range and deviation of soccer balls and volleyballs were 34.4 m and 38.6 m and 19.7 and 21.4 degrees, respectively. The main effects of the ball type, shot speed and spin were significant (

Shot Noise with Interaction Effects in Single Walled Carbon Nanotubes

We have measured shot noise in single walled carbon nanotubes (SWNT) with good contacts at 4.2 K at low frequencies ($f=600 - 850$ MHz). We find a strong modulation of shot noise over the Fabry-Perot pattern; in terms of differential Fano factor the variation ranges over 0.4 - 1.2. The shot noise variation, in combination with differential conductance, is analyzed using two (spin-degenerate) modes with different, energy-dependent transmission coefficients. No power law dependence of shot noise, as expected for Luttinger liquids, was found in our measurements.Comment: 5 pages, 4 figure

Determination of helicities in unidirectional assemblies of graphitic or graphiticlike tubular structures

Here we propose a universal method for the determination of all helicities present in unidirectional assemblies of hexagon-based graphitic or graphiticlike tubular structures, e.g., multiwalled or bundled carbon nanotubes(CNTs) or boron-nitride nanotubes and their structural analogs. A critical dimension characteristic of a fundamental structural property, i.e., the atomic bond length, is discerned from electron diffraction patterns by which all helicities present in the assemblies are identified. Using this method, we determine the helicity population in a single-walled CNT sample produced by laser ablation technique.Peer reviewe

Coulomb blockade in one-dimensional arrays of high conductance tunnel junctions

Properties of one-dimensional (1D) arrays of low Ohmic tunnel junctions (i.e. junctions with resistances comparable to, or less than, the quantum resistance $R_{\rm q}\equiv h/e^2\approx 25.8$ k$\Omega$) have been studied experimentally and theoretically. Our experimental data demonstrate that -- in agreement with previous results on single- and double-junction systems -- Coulomb blockade effects survive even in the strong tunneling regime and are still clearly visible for junction resistances as low as 1 k$\Omega$. We have developed a quasiclassical theory of electron transport in junction arrays in the strong tunneling regime. Good agreement between the predictions of this theory and the experimental data has been observed. We also show that, due to both heating effects and a relatively large correction to the linear relation between the half-width of the conductance dip around zero bias voltage, $V_{1/2}$, and the measured electronic temperature, such arrays are inferior to those conventionally used in the Coulomb Blockade Thermometry (CBT). Still, the desired correction to the half-width, $\Delta V_{1/2}$, can be determined rather easily and it is proportional to the magnitude of the conductance dip around zero bias voltage, $\Delta G$. The constant of proportionality is a function of the ratio of the junction and quantum resistances, $R/R_{\rm q}$, and it is a pure strong tunneling effect.Comment: LaTeX file + five postscript figure

Robust Bessel-function-based method for determination of the (n, m) indices of single-walled carbon nanotubes by electron diffraction

We report a calibration-free method for the determination of chiral indices (n,m) of single-walled carbon nanotubes from their electron diffraction patterns based on Bessel function analysis of the diffracted layer lines. An approach has been developed for confident identification of the orders of the Bessel functions from the intensity modulations of the diffraction layer lines, to which (n,m) are correlated. In particular, we critically evaluate the effect of nanotube inclination on the validity of the method and show that the layer lines governed by high-order Bessel functions tolerate higher tilt angles than those of low-order Bessel functions and thus are favored for (n,m) evaluation. The method is of particular significance in that it considerably enhances the precision of chiral indexing and makes possible the analysis of high-order Bessel functions, especially when EDPs are of relatively low pixel resolution. The technique can be extended to structural analysis of double-walled carbon nanotubes.Peer reviewe

Effect of quantum noise on Coulomb blockade in normal tunnel junctions at high voltages

We have investigated asymptotic behavior of normal tunnel junctions at voltages where even the best ohmic environments start to look like RC transmission lines. In the experiments, this is manifested by an exceedingly slow approach to the linear behavior above the Coulomb gap. As expected on the basis of the quantum theory taking into account interaction with the environmental modes, better fits are obtained using 1/sqrt{V}- than 1/V- dependence for the asymptote. These results agree with the horizon picture if the frequency-dependent phase velocity is employed instead of the speed of light in order to determine the extent of the surroundings seen by the junction.Comment: 9 pages, 4 figures, submitted to Phys. Rev.

Prevalence of obesity and disturbances in glucose homeostasis in HIV-infected subjects and general population - missed diagnoses of diabetes?

Objectives Comparative data on glucose disorders using fasting blood samples between people living with HIV (PLWH) and the general population are lacking. The objective of this study was to compare the prevalence and risk factors of obesity and disturbances in glucose homeostasis between PLWH treated with modern antiretroviral therapy and the general population. Methods Adjusted prevalence of obesity, features of insulin resistance (triglyceride:high-density lipoprotein cholesterol ratio and alanine aminotransferase), impaired fasting glucose (IFG), diabetes mellitus (DM) and combined dysglycaemia (presence of IFG or DM) were determined using fasting blood samples among 1041 PLWH and 7047 subjects representing the general population. Results People living with HIV had a lower prevalence of obesity [18.2%, 95% confidence interval (CI): 15.1-21.2 vs. 23.9%, 95% CI: 22.4-25.4], but a higher prevalence of insulin resistance and IFG (20.0%, 95% CI: 16.6-23.4 vs. 9.8%, 95% CI: 8.7-10.8) than the general population. Fasting glucose concentration was higher, but glycated haemoglobin (HbA1c) was lower, among PLWH. Prevalence of dysglycaemia for a given body mass index (BMI) was higher in PLWH than in the general population. The prevalence of DM did not differ between PLWH (13.2%, 95% CI: 10.2-15.9) and the general population (14.5%, 95% CI: 13.6-15.4). Conclusions The prevalence of obesity was lower, but the risk of dysglycaemia for a given BMI was significantly higher, among PLWH, highlighting the importance of prevention and treatment of obesity among HIV-infected subjects. Regardless of the increased prevalence of insulin resistance and IFG, DM was surprisingly not more common among PLWH, raising concern about the under-diagnosis of DM, possibly due to low sensitivity of HbA1c in this patient population.Peer reviewe