1,387 research outputs found
Cyclic motion control for programmable bevel-tip needles 3D steering: a simulation study
Flexible, steerable, soft needles are desirable in Minimally Invasive Surgery to achieve complex trajectories while maintaining the benefits of percutaneous intervention compared to open surgery. One such needle is the multi-segment Programmable Bevel-tip Needle (PBN), which is inspired by the mechanical design of the ovipositor of certain wasps. PBNs can steer in 3D whilst minimizing the force applied to the surrounding substrate, due to the cyclic motion of the segments. Taking inspiration also from the control strategy of the wasp to perform insertions and lay their eggs, this paper presents the design of a cyclic controller that can steer a PBN to produce a desired trajectory in 3D. The performance of the controller is demonstrated in simulation in comparison to that of a direct controller without cyclic motion. It is shown that, while the same steering curvatures can be attained by both controllers, the time taken to achieve the configuration is longer for the cyclic controller, leading to issues of potential under-steering and longer insertion times
Fishes of the Charlotte Harbor Estuarine System, Florida
To date, 255 fish species in 95 families have been reliably reported from the Charlotte Harbor estuarine system in southwest Florida. The species list was compiled from recent fishery-independent collections, a review of reports and peer-reviewed literature, and examination of cataloged specimens at the Florida Museum of Natural History. Thirty-nine species are new records for this estuarine system. Many of the newly documented species are common on the west Florida continental shelf and associated inshore habitats. Twenty-two previously reported species were not included in the species list presented herein on the basis of more recent research, doubtful original identifications, or questionable locality data
Calibration of centre-of-mass energies at LEP 2 for a precise measurement of the W boson mass
The determination of the centre-of-mass energies for all LEP 2 running is
presented. Accurate knowledge of these energies is of primary importance to set
the absolute energy scale for the measurement of the W boson mass. The beam
energy between 80 and 104 GeV is derived from continuous measurements of the
magnetic bending field by 16 NMR probes situated in a number of the LEP
dipoles. The relationship between the fields measured by the probes and the
beam energy is defined in the NMR model, which is calibrated against precise
measurements of the average beam energy between 41 and 61 GeV made using the
resonant depolarisation technique. The validity of the NMR model is verified by
three independent methods: the flux-loop, which is sensitive to the bending
field of all the dipoles of LEP; the spectrometer, which determines the energy
through measurements of the deflection of the beam in a magnet of known
integrated field; and an analysis of the variation of the synchrotron tune with
the total RF voltage. To obtain the centre-of-mass energies, corrections are
then applied to account for sources of bending field external to the dipoles,
and variations in the local beam energy at each interaction point. The relative
error on the centre-of-mass energy determination for the majority of LEP 2
running is 1.2 x 10^{-4}, which is sufficiently precise so as not to introduce
a dominant uncertainty on the W mass measurement.Comment: 79 pages, 45 figures, submitted to EPJ
Observation of radiative spin-polarization at 60.6 GeV
Radiative spin-polarization has been used extensively at LEP to accurately measure the beam energy around the Z resonance. As the LEP physics has moved on to the W boson the calibration based on polarization must be extended towards higher beam energies. This is difficult as the depolarizing effects of spin resonances grow rapidly with beam energy. At LEP it has been possible for the first time to measure transverse beam polarization at 60.6 GeV. To allow a build-up of polarization the tunes and the energy were chosen accurately. A low phase advance optics was used and careful orbit correction was carried out using dynamic beam based alignment data. Harmonic spin matching was applied both in a deterministic and a novel semi- empirical way. (11 refs)
Spatial Resolution of Double-Sided Silicon Microstrip Detectors for the PAMELA Apparatus
The PAMELA apparatus has been assembled and it is ready to be launched in a
satellite mission to study mainly the antiparticle component of cosmic rays. In
this paper the performances obtained for the silicon microstrip detectors used
in the magnetic spectrometer are presented. This subdetector reconstructs the
curvature of a charged particle in the magnetic field produced by a permanent
magnet and consequently determines momentum and charge sign, thanks to a very
good accuracy in the position measurements (better than 3 um in the bending
coordinate). A complete simulation of the silicon microstrip detectors has been
developed in order to investigate in great detail the sensor's characteristics.
Simulated events have been then compared with data gathered from minimum
ionizing particle (MIP) beams during the last years in order to tune free
parameters of the simulation. Finally some either widely used or original
position finding algorithms, designed for such kind of detectors, have been
applied to events with different incidence angles. As a result of the analysis,
a method of impact point reconstruction can be chosen, depending on both the
particle's incidence angle and the cluster multiplicity, so as to maximize the
capability of the spectrometer in antiparticle tagging.Comment: 28 pages, 18 figures, submitted to Nuclear Instruments and Methods in
Physics Research
Helium Emission in the Type Ic SN 1999cq
We present the first unambiguous detection of helium emission lines in
spectra of Type Ic supernovae (SNe Ic). The presence of He I lines, with full
width at half maximum ~ 2000 km/s, and the distinct absence of any other
intermediate-width emission (e.g., Halpha), implies that the ejecta of SN Ic
1999cq are interacting with dense circumstellar material composed of almost
pure helium. This strengthens the argument that the progenitors of SNe Ic are
core-collapse events in stars that have lost both their hydrogen and helium
envelopes, either through a dense wind or mass-transfer to a companion. In this
way, SN 1999cq is similar to supernovae such as SN 1987K and SN 1993J that
helped firmly establish a physical connection between Type Ib and Type II
supernovae. The light curve of SN 1999cq is very fast, with an extremely rapid
rise followed by a quick decline. SN 1999cq is also found to exhibit a high
level of emission at blue wavelengths (< 5500 A), likely resulting from either
an unusually large amount of iron and iron-group element emission or
uncharacteristically low reddening compared with other SNe Ic.Comment: 17 pages (AASTeX V5.0), 4 figures, accepted for publication in the
Astronomical Journa
The Spectroscopic Variability of GRB 021004
We present spectra of the optical transient (OT) associated with GRB 021004.
The spectra show a blue continuum with superposed absorption features and one
emission line. We confirm two intervening metal-line systems at z = 1.380 and z
= 1.602 and one very strong absorption system at a redshift of z = 2.323.
Ly_alpha emission is also seen at this redshift. While the spectrum of the OT
overall cannot be simply described with a power law, the spectral index over
the range 5500-8850 A is steep, F_nu ~ nu^(-0.96 +/- 0.03). Comparison of
spectra from multiple epochs shows a distinct color evolution with the OT
becoming redder with time over the first three days. This is the first clear
example of color change in an OT detected spectroscopically.Comment: 13 pages, two figures, revised per referee's comments, accepted for
publication in ApJ Letter
The Type IIn SN 1995G: Interaction with the CSM
We present the photometric and spectroscopic evolution of the type IIn SN
1995G in NGC 1643, on the basis of 4 years of optical and infrared
observations. This supernova shows very flat optical light curves similar to SN
1988Z, with a slow decline rate at all times. The spectra are characterized by
strong Balmer lines with multiple components in emission and with a P-Cygni
absorption component blueshifted by only 700 km/s. This feature indicates the
presence of a slowly expanding shell above the SN ejecta as in the case of SNe
1994aj and 1996L. As in other SNe IIn the slow luminosity decline cannot be
explained only with a radioactive energy input and an additional source of
energy is required, most likely that produced by the interaction between
supernova ejecta and a pre--existent circumstellar medium. It was estimated
that the shell material has a density n(H) >> 10^8 cm^-3, consistent with the
absence of forbidden lines in the spectra. About 2 years after the burst the
low velocity shell is largely overtaken by the SN ejecta and the luminosity
drops at a faster rate.Comment: 14 pages, including 11 figures. Accepted by MNRA
Optical Spectra of the Type Ia Supernova 1998aq
We present 29 optical spectra of the normal Type Ia SN 1998aq, ranging from 9
days before to 241 days after the time of maximum brightness. This
spectroscopic data set, together with photometric data presented elsewhere,
makes SN 1998aq one of the best observed Type Ia supernova at optical
wavelengths. We use the parameterized supernova synthetic-spectrum code SYNOW
to study line identifications in the early photospheric-phase spectra. The
results include evidence for lines of singly ionized carbon, at ejection
velocities as low as 11,000 km/sec. Implications for explosion models are
discussed.Comment: 40 pages including 20 figures and 4 tables. Accepted by A
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