197,596 research outputs found
Photoactivatable metal complexes : from theory to applications in biotechnology and medicine
This short review highlights some of the exciting new experimental and theoretical developments in the field of photoactivatable metal complexes and their applications in biotechnology and medicine. The examples chosen are based on some of the presentations at the Royal Society Discussion Meeting in June 2012, many of which are featured in more detail in other articles in this issue. This is a young field. Even the photochemistry of well-known systems such as metalâcarbonyl complexes is still being elucidated. Striking are the recent developments in theory and computation (e.g. time-dependent density functional theory) and in ultrafast-pulsed radiation techniques which allow photochemical reactions to be followed and their mechanisms to be revealed on picosecond/nanosecond time scales. Not only do some metal complexes (e.g. those of Ru and Ir) possess favourable emission properties which allow functional imaging of cells and tissues (e.g. DNA interactions), but metal complexes can also provide spatially controlled photorelease of bioactive small molecules (e.g. CO and NO)âa novel strategy for site-directed therapy. This extends to cancer therapy, where metal-based precursors offer the prospect of generating excited-state drugs with new mechanisms of action that complement and augment those of current organic photosensitizers
Compression properties of polymeric syntactic foam composites under cyclic loading
Syntactic foams are composite materials frequently used in applications
requiring the properties of low density and high damage tolerance. In the
present work, polymer-based syntactic foams were studied under cyclic
compression in order to investigate their compressibility, recoverability,
energy dissipation and damage tolerance. These syntactic foams were
manufactured by adding hollow polymer microspheres of various sizes and wall
thicknesses into a polyurethane matrix. The associated loading and unloading
curves during cyclic testing were recorded, revealing the viscoelastic nature
of the materials. SEM images of the samples were obtained in order to study
potential damage mechanisms during compression. It was observed that these
syntactic foams exhibit high elastic recovery and energy dissipation over a
wide range of compressional strains and the addition of polymer microspheres
mitigate the damage under compressional loading.Comment: 25 pages, 13 figure
XTE J1739-302 as a Supergiant Fast X-ray Transient
XTE J1739-302 is a transient X-ray source with unusually short outbursts,
lasting on the order of hours. Here we give a summary of X-ray observations we
have made of this object in outburst with the Rossi X-ray Timing Explorer
(RXTE) and at a low level of activity with the Chandra X-ray Observatory, as
well as observations made by other groups. Visible and infrared spectroscopy of
the mass donor of XTE J1739-302 are presented in a companion paper. The X-ray
spectrum is hard both at low levels and in outburst, but somewhat variable, and
there is strong variability in the absorption column from one outburst to
another. Although no pulsation has been observed, the outburst data from
multiple observatories show a characteristic timescale for variability on the
order of 1500-2000 s. The Chandra localization (right ascension 17h 39m 11.58s,
declination -30o 20' 37.6'', J2000) shows that despite being located less than
2 degrees from the Galactic Center and highly absorbed, XTE J1739-302 is
actually a foreground object with a bright optical counterpart. The combination
of a very short outburst timescale and a supergiant companion is shared with
several other recently-discovered systems, forming a class we designate as
Supergiant Fast X-ray Transients (SFXTs). Three persistently bright X-ray
binaries with similar supergiant companions have also produced extremely short,
bright outbursts: Cyg X-1, Vela X-1, and 1E 1145.1-6141.Comment: 16 pages, 7 figures, 2 tables, in press in The Astrophysical Journal;
see also the companion paper by Negueruela et a
Coulomb interactions in single, charged self-assembled quantum dots: radiative lifetime and recombination energy
We present results on the charge dependence of the radiative recombination
lifetime, Tau, and the emission energy of excitons confined to single
self-assembled InGaAs quantum dots. There are significant dot-to-dot
fluctuations in the lifetimes for a particular emission energy. To reach
general conclusions, we present the statistical behavior by analyzing data
recorded on a large number of individual quantum dots. Exciton charge is
controlled with extremely high fidelity through an n-type field effect
structure, providing access to the neutral exciton (X0), the biexciton (2X0)
and the positively (X1+) and negatively (X1-) charged excitons. We find
significant differences in the recombination lifetime of each exciton such
that, on average, Tau(X1-) / Tau(X0) = 1.25, Tau(X1+) / Tau(X0) = 1.58 and
Tau(2X0) / Tau(X0) = 0.65. We attribute the change in lifetime to significant
changes in the single particle hole wave function on charging the dot, an
effect more pronounced on charging X0 with a single hole than with a single
electron. We verify this interpretation by recasting the experimental data on
exciton energies in terms of Coulomb energies. We show directly that the
electron-hole Coulomb energy is charge dependent, reducing in value by 5-10% in
the presence of an additional electron, and that the electron-electron and
hole-hole Coulomb energies are almost equal.Comment: 8 pages, 7 figures, submitted to Phys. Rev.
Identification of the X-ray pulsar in Hercules: A new optical pulsar
A series of photographic, photoelectric, and spectroscopic observations beginning June 1, 1972 has led to the optical identification of Her X-1 (2U 1705 + 34), a pulsed X-ray source in an eclipsing binary system, with the thirteenth magnitude blue variable star HZ Herculis. The detection of optical pulses at the frequency of the X-ray pulsar on three nights makes the identification conclusive and establishes HZ Her as the second known optical pulsar. The strength of the optical pulses may be correlated with the orbital phase but is not obviously related to the high or low intensity states of the X-ray source
Optimum take-off angle in the long jump
In this study, we found that the optimum take-off angle for a long jumper may be predicted by combining the equation for the range of a projectile in free flight with the measured relations between take-off speed, take-off height and take-off angle for the athlete. The prediction method was evaluated using video measurements of three experienced male long jumpers who performed maximum-effort jumps over a wide range of take-off angles. To produce low take-off angles the athletes used a long and fast run-up, whereas higher take-off angles were produced using a progressively shorter and slower run-up. For all three athletes, the take-off speed decreased and the take-off height increased as the athlete jumped with a higher take-off angle. The calculated optimum take-off angles were in good agreement with the athletes' competition take-off angles
NGC1333/IRAS4: A multiple star formation laboratory
We present SCUBA observations of the protomultiple system NGC1333/IRAS4 at
450um and 850um. The 850um map shows significant extended emission which is
most probably a remnant of the initial cloud core. At 450um, the component 4A
is seen to have an elongated shape suggestive of a disk. Also we confirm that
in addition to the 4A and 4B system, there exists another component 4C, which
appears to lie out of the plane of the system and of the extended emission.
Deconvolution of the beam reveals a binary companion to IRAS4B. Simple
considerations of binary dynamics suggest that this triple 4A-4BI-4BII system
is unstable and will probably not survive in its current form. Thus IRAS4
provides evidence that systems can evolve from higher to lower multiplicity as
they move towards the main sequence. We construct a map of spectral index from
the two wavelengths, and comment on the implications of this for dust evolution
and temperature differences across the map. There is evidence that in the
region of component 4A the dust has evolved, probably by coagulating into
larger or more complex grains. Furthermore, there is evidence from the spectral
index maps that dust from this object is being entrained in its associated
outflow.Comment: 10 pages, 10 figures. To appear in MNRAS. Uses mn.sty. Also available
at http://www.astro.phys.ethz.ch/papers/smith/smith_p_m.htm
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