Colloidal stability of nanoparticles derived from simulated cloud-processed mineral dusts

Laboratory simulation of cloud processing of three model dust types with distinct Fe-content (Moroccan dust, Libyan dust and Etna ash) and reference goethite and ferrihydrite were conducted in order to gain a better understanding of natural nanomaterial inputs and their environmental fate and bioavailability. The resulting nanoparticles (NPs) were characterised for Fe dissolution kinetics, aggregation/size distribution, micromorphology and colloidal stability of particle suspensions using a multi-method approach. We demonstrated that the: (i) acid-leachable Fe concentration was highest in volcanic ash (1 m Mg(-1) dust) and was followed by Libyan and Moroccan dust with an order of magnitude lower levels; (ii) acid leached Fe concentration in the<20 nm fraction was similar in samples processed in the dark with those under artificial sunlight, but average hydrodynamic diameter of NPs after cloud-processing (pH~6) was larger in the former; iii) NPs formed at pH~6 were smaller and less poly-disperse than those at low pH, whilst unaltered zeta potentials indicated colloidal instability; iv) relative Fe percentage in the finer particles derived from cloud processing does not reflect Fe content of unprocessed dusts (e.g. volcanic ash>Libyan dust). The common occurrence of Fe-rich "natural nanoparticles" in atmospheric dust derived materials may indicate their more ubiquitous presence in the marine environment than previously thought.

The Sports Overload Injuries of the Lower Extremities from the Biomechanical Point of View

This work studies the major sports overload injuries of the lower extremities from the biomechanical point of view. At the same time, the main paradigms of podiatric biomechanics and the application of new biomechanical theories in the study of these lesions are reviewed. With current legislation, clinical gait biomechanical studies should be carried out in health centres and the only health professionals who can perform them are podiatrists and doctors (because they both can diagnose). Graduates in physical education can carry out studies in the field or in the sports court for the sole purpose of improving athletic performance, but never intended to treat a pathology overload.

ShCal04 Southern Hemisphere Calibration, 0–11.0 Cal Kyr BP

Recent measurements on dendrochronologically-dated wood from the Southern Hemisphere have shown that there are differences between the structural form of the radiocarbon calibration curves from each hemisphere. Thus, it is desirable, when possible, to use calibration data obtained from secure dendrochronologically-dated wood from the corresponding hemisphere. In this paper, we outline the recent work and point the reader to the internationally recommended data set that should be used for future calibration of Southern Hemisphere 14C dates.

Performance analysis of an improved power-saving medium access protocol for IEEE 802.11 point coordination function WLAN

Wireless enabled portable devices must operate with the highest possible energy efficiency while still maintaining a minimum level and quality of service to meet the user's expectations. The authors analyse the performance of a new pointer-based medium access control protocol that was designed to significantly improve the energy efficiency of user terminals in wireless local area networks. The new protocol, pointer controlled slot allocation and resynchronisation protocol (PCSAR), is based on the existing IEEE 802.11 point coordination function (PCF) standard. PCSAR reduces energy consumption by removing the need for power saving stations to remain awake and listen to the channel. Using OPNET, simulations were performed under symmetric channel loading conditions to compare the performance of PCSAR with the infrastructure power saving mode of IEEE 802.11, PCF-PS. The simulation results demonstrate a significant improvement in energy efficiency without significant reduction in performance when using PCSAR. For a wireless network consisting of an access point and 8 stations in power saving mode, the energy saving was up to 31% while using PCSAR instead of PCF-PS, depending upon frame error rate and load. The results also show that PCSAR offers significantly reduced uplink access delay over PCF-PS while modestly improving uplink throughput.

HST/STIS observations of the high-velocity interstellar cloud HVC 291.2-41.2+80: a warm, mainly ionized high-velocity cloud

We present intermediate-resolution HST/STIS spectra of a high- velocity interstellar cloud ((LSR)-L-upsilon = + 80 kms(-1)) towards DI1388, a young star in the Magellanic Bridge located between the Small and Large Magellanic Clouds. The STIS data have a signal-to-noise ratio (S/N) of 20-45 and a spectral resolution of about 6.5 km s(-1) (FWHM), The high-velocity cloud absorption is observed in the lines of C II, O I, Si II, Si III, Si IV and S III. Limits can be placed on the amount of S II and Fe II absorption that is present. An analysis of the relative abundances derived from the observed species, particularly C II and O I, suggests that this high-velocity gas is warm (T-k similar to 10(3)-10(4) K) and predominantly ionized, This hypothesis is supported by the presence of absorption produced by highly ionized species, such as Si IV, This sightline also intercepts two other high-velocity clouds that produce weak absorption features at (LSR)-L-upsilon = + 113 and + 130kms(-1) in the STIS spectra.

Optical spectroscopy of the M 15 intermediate velocity cloud

We present echelle spectrograph observations in the Na D lines, at resolutions of 6.2-8.5 km s(-1), for 11 stars located in the line-of-sight to the M15 intermediate velocity cloud (IVC), which has a radial velocity of similar to +70 km s(-1) in the Local Standard of Rest. This cloud is a part of IVC Complex gp. The targets range in magnitude from m(V) = 13.3-14.8. Seven of the observed stars are in the M15 globular cluster, the remaining four being field stars. Three of the observed cluster stars are located near a peak in intensity of the IVC Hi column density as observed at a resolution of similar to 1 arcmin. Intermediate velocity gas is detected in absorption towards 7 stars, with equivalent widths in NaD2 ranging from similar to0.09-0.20 Angstrom, corresponding to log(10)(N-Na cm(-2)) similar to 11.8-12.5, and Na I/H I column density ratios (neglecting the HII component) ranging from similar to(1-3) x 10(-8). Over scales ranging from 30 arcsec to 1 arcmin, the Na i column density and the Na i/H i ratio varies by upto 70 per cent and a factor of similar to 2, respectively. Combining the current sightlines with previously obtained Nai data from Kennedy et al. (1998b), the Na i/H i column density ratio over cluster sightlines varies by upto a factor of similar to 25, when using Hi data of resolution similar to 2 x 1 arcmin. One cluster star, M15 ZNG-1, was also observed in the Ca i (lambda(air) = 4226.728 Angstrom) and Ca ii (lambda(air) = 3933.663 Angstrom) lines. A column density ratio N(Ca i)/N(Ca ii) <0.03 was found, typical of values seen in the warm ionised interstellar medium. Towards this sightline, the IVC has a Nai/Ca ii column density ratio of &SIM; 0.25, similar to that observed in the local interstellar medium. Finally, we detect tentative evidence for IV absorption in Ki (?(air) = 7698:974 &ANGS) towards 3 cluster stars, which have N(K i)/N(H i) ratios of &SIM;0.5-3 x 10(-9).

HI and optical spectroscopy towards the M15 intermediate- velocity cloud

We present single-dish Arecibo 21-cm H i observations, covering a 0 degrees 675x0 degrees 625 RA-Dec. grid, of the intermediate-velocity cloud (IVC) centred upon the M15 globular cluster. The velocity and positional structure of the IVC gas at V-LSR=70 km s(-1) are investigated; it is found to be clumpy and has a peak surface density N(H i)similar to 8x10(19) cm(- 2). Additionally, we have performed a long H i integration towards HD 203664, a Galactic halo star some 3 degrees1 from M15, in which optical IVC absorption has previously been detected. No H i with a velocity exceeding 60 km s(-1) was found to a brightness temperature limit of 0.05 K. However, additional pointings did detect IVC gas approximately mid-way between HD 203664 and M15. Finally, we present both Arecibo H i pointings and low-resolution spectra in the Ca ii H and K lines towards 15 field stars in the general field towards M15, in an attempt to obtain the distance to the IVC. Intermediate- velocity H i is detected towards seven sightlines. Stellar spectral types are derived for 12 of the sample. Assuming that these stars lie on the main sequence, their distances are estimated to lie in the range 150 less than or equal tod less than or equal to 1350 pc. No Ca ii absorption is observed, either because the IVC is further away than similar to 1350 pc or more likely because the gas along these sightlines is of too low a density to be detected by the current observations.

HI observations of the high-velocity cloud in the direction of M 92

We present wide-field neutral hydrogen (H I) Lovell telescope multibeam, and Dominion Radio Astrophysical Observatory Hi synthesis observations, of the high velocity cloud (HVC) located in the general direction of the globular cluster M92. This cloud is part of the larger Complex C and lies at velocities between similar to -80 and -130 km s(-1) in the Local Standard of Rest. The Lovell telescope observations, of resolution 12 arcmin spatially and 3.0 km s(-1) in velocity, fully sampling a 3.1 degrees x 12.6 degrees RA-Dec grid, have found that this part of HVC Complex C comprises two main condensations, lying approximately north-south in declination, separated by similar to2 degrees and being parallel to the Galactic plane. At this resolution, peak values of the brightness temperature and Hi column density of similar to1.4 K and similar to5 x 10(19) cm(-2) are determined, with relatively high values of the full width half maximum velocity (FWHM) of similar to 22 km s(-1) being observed, equivalent to a gas kinetic temperature, in the absence of turbulence and geometric effects of similar to 10 000 K. Each of these properties, as well as the sizes of the clouds, are similar in the two components. The DRAO observations, towards the Northern HVC condensation, are the first high-resolution Hi spectra of Complex C. When smoothed to a resolution of 3 arcmin, they identify several Hi intensity peaks with column densities in the range 4-7 x 10(19) cm(-2). Further smoothing of these data to 6 arcmin resolution tentatively indicates that parts of the HVC consist of two velocity components, of similar brightness temperature, separated by similar to7 km s(-1) in velocity, and with FWHM velocity widths of similar to5-7 km s(-1). No IRAS 60 or 100 micron flux is associated with the M92 HVC. Cloud properties are briefly discussed and compared to previous observations of HVCs.

An exactly solvable four transition point model

Heavy particle collisions, in particular low-energy ion-atom collisions, are amenable to semiclassical JWKB phase integral analysis in the complex plane of the internuclear separation. Analytic continuation in this plane requires due attention to the Stokes phenomenon which parametrizes the physical mechanisms of curve crossing, non-crossing, the hybrid Nikitin model, rotational coupling and predissociation. Complex transition points represent adiabatic degeneracies. In the case of two or more such points, the Stokes constants may only be completely determined by resort to the so-called comparison- equation method involving, in particular, parabolic cylinder functions or Whittaker functions and their strong-coupling asymptotics. In particular, the Nikitin model is a two transition-point one-double-pole problem in each half-plane corresponding to either ingoing or outgoing waves. When the four transition points are closely clustered, new techniques are required to determine Stokes constants. However, such investigations remain incomplete, A model problem is therefore solved exactly for scattering along a one-dimensional z-axis. The energy eigenvalue is b(2)-a(2) and the potential comprises -z(2)/2 (parabolic) and -a(2) + b(2)/2z(2) (centrifugal/centripetal) components. The square of the wavenumber has in the complex z-plane, four zeros each a transition point at z = +/-a +/- ib and has a double pole at z = 0. In cases (a) and (b), a and b are real and unitarity obtains. In case (a) the reflection and transition coefficients are parametrized by exponentials when a(2) + b(2) > 1/2. In case (b) they are parametrized by trigonometrics when a(2) + b(2) <1/2 and total reflection is achievable. In case (c) a and b are complex and in general unitarity is not achieved due to loss of flux to a continuum (O'Rourke and Crothers, 1992 Proc. R. Sec. 438 1). Nevertheless, case (c) coefficients reduce to (a) or (b) under appropriate limiting conditions. Setting z = ht, with h a real constant, an attempt is made to model a two-state collision problem modelled by a pair of coupled first-order impact parameter equations and an appropriate (T) over tilde-tau relation, where (T) over tilde is the Stueckelberg variable and tau is the reduced or scaled time. The attempt fails because (T) over tilde is an odd function of tau, which is unphysical in a real collision problem. However, it is pointed out that by applying the Kummer exponential model to each half-plane (O'Rourke and Crothers 1994 J. Phys. B: At. Mel. Opt. Phys. 27 2497) the current model is in effect extended to a collision problem with four transition points and a double pole in each half-plane. Moreover, the attempt in itself is not a complete failure since it is shown that the result is a perfect diabatic inelastic collision for a traceless Hamiltonian matrix, or at least when both diagonal elements are odd and the off-diagonal elements equal and even.

B-type supergiants in the Small Magellanic Cloud: rotational velocities and implications for evolutionary models

High-resolution spectra for 24 SMC and Galactic B-type supergiants have been analysed to estimate the contributions of both macroturbulence and rotation to the broadening of their metal lines. Two different methodologies are considered, viz. goodness-of-fit comparisons between observed and theoretical line profiles and identifying zeros in the Fourier transforms of the observed profiles. The advantages and limitations of the two methods are briefly discussed with the latter techniques being adopted for estimating projected rotational velocities ( v sin i) but the former being used to estimate macroturbulent velocities. The projected rotational velocity estimates range from approximately 20 to 60 kms(-1), apart from one SMC supergiant, Sk 191, with a v sin i similar or equal to 90 km s(-1). Apart from Sk 191, the distribution of projected rotational velocities as a function of spectral type are similar in both our Galactic and SMC samples with larger values being found at earlier spectral types. There is marginal evidence for the projected rotational velocities in the SMC being higher than those in the Galactic targets but any differences are only of the order of 5 - 10 km s(-1), whilst evolutionary models predict differences in this effective temperature range of typically 20 to 70 km s(-1). The combined sample is consistent with a linear variation of projected rotational velocity with effective temperature, which would imply rotational velocities for supergiants of 70 kms(-1) at an effective temperature of 28 000 K ( approximately B0 spectral type) decreasing to 32 km s(-1) at 12 000 K (B8 spectral type). For all targets, the macroturbulent broadening would appear to be consistent with a Gaussian distribution ( although other distributions cannot be discounted) with an 1/e half-width varying from approximately 20 km s(-1) at B8 to 60 km s(-1) at B0 spectral types.

Pulsed evaporative cooling of ion cloud in an electron beam ion trap

A technique for producing cold ensembles of trapped highly charged ions is described. The ions, trapped in an electron beam ion trap, can undergo a drastic contraction during the pulsed mode of evaporative cooling, if a truncated Boltzmann distribution is assumed. The underlying theory and the experimental results are presented.