152 research outputs found
CCD photometry and new models of 5 minor planets
We present new R filtered CCD observations of 5 faint and moderately faint
asteroids carried out between October, 1998 and January, 1999. The achieved
accuracy is between 0.01-0.03 mag, depending mainly on the target brightness.
The obtained sinodic periods and amplitudes:
683 Lanzia - 4.6+/-0.2 h, 0.13 mag; 725 Amanda - >3.0 h, >=0.40 mag; 852
Wladilena - 4.62+/-0.01 h, 0.32 mag (December, 1998) and 0.27 mag (January,
1999); 1627 Ivar - 4.80+/-0.01, 0.77 mag (December, 1998) and 0.92 mag
(January, 1999). The Near Earth Object 1998 PG unambiguously showed
doubly-periodic lightcurve, suggesting the possibility of a relatively fast
precession (P_1=1.3 h, P_2=5.3 h).
Collecting all data from the literature, we determined new models for 3 minor
planets. The resulting spin vectors and triaxial ellipsoids have been
calculated by an amplitude-method. Sidereal periods and senses of rotation were
calculated for two asteroids (683 and 1627) by a modified epoch-method. The
results are:
683 - lambda_p=15/195+/-25 deg, beta_p=52+/-15 deg, a/b=1.15+/-0.05,
b/c=1.05+/-0.05, P_sid=0.1964156+/-0.0000001 d, retrograde; 852 -
lambda_p=30/210+/-20 deg, beta_p=30+/-10 deg, a/b=2.3+/-0.3, b/c=1.2+/-0.2;
1627 - lambda_p=145/325+/-8 deg, beta_p=34+/-6 deg, a/b=2.0+/-0.1,
b/c=1.09+/-0.05, P_sid=0.1999154+/-0.0000003 d, retrograde. The obtained shape
of 1627 is in good agreement with radar images by Ostro et al. (1990).Comment: 8 pages, accepted for publication in Astronomy and Astrophysics
Suppl. Serie
The Problem of Solving Fracture of the Denture Base in Preedentulous States
The mechanical fatigue resistance of the denture base seems to be a neglected part of treatment planning. Extreme overload can occur, which is only evaluated in the case of fracture. In full or partial edentia the dental base can be exposed to an extreme stress concentration which may be coupled with the incidental source of failure during processing of the denture. The aim of this lecture is to report cases, where we were able to overcome dental base fracture, which had not been foreseen earlier. In the first case a history of several fractures of an upper complete denture is presented. Metal net, framework and incorporation of glass fibres and reline were
stages of the instructive problem solving process. In the second case a man wearing an overdenture with ball attachments under implant fixtures is presented. After multiple fractures of the dental base we used glass fibre reinforcement for repair. After this procedure there was an eventless period, which proves the mechanical resistance
of the denture base. In the third case presented both the denture base and the acrylic tooth were damaged. The multiple fracture
could also be treated with glass fibre reinforcement, which was successful. From these cases we concluded:
1. Careful case history and treatment plan could have helped to overcome the subsequent problems.
2. The clinical implication is that the glass fibre reinforcement can provide effective strength for the denture base. We could not neglect evaluation of the mucosa and bone support.
In the following period we reinforced new dentures preventively with fibres in 15 cases. At the same time we also continued the repair the broken dentures of 10
patients. The outcome exceeded our greatest expectations: no fracture was seen. However, further study is needed to extend the observation period
Photometry of SN 2002bo with template image subtraction
VRI photometry of the type Ia supernova 2002bo is presented. This SN exploded
in a dusty region of the host galaxy NGC 3190, thus, subtraction of a template
frame was necessary to obtain reliable photometry. We used a template frame of
NGC 3190 taken during the course of our galaxy imaging project, fortunately,
just a few days before SN 2002bo was discovered. The aim of this project is to
collect template frames of nearby galaxies that are potential hosts of bright
SNe. Subtraction of pre-SN images helped us to exclude the background light
contamination of the host galaxy. The maximum occurred at JD 2452346, with
maximal V brightness of 13.58. MLCS analysis led to T0(B)=JD 2452346.1 pm 0.8
(fiducial B-maximum), E(B-V)=0.24 pm 0.02, mu0=32.46 pm 0.06, Delta=-0.14 pm
0.04. E(B-V)=0.24(2) indicates a significant extinction in the host galaxy as
the galactic reddening is negligible toward NGC 3190. The accepted value of
Delta indicates that SN 2002bo was a slightly overluminous SN by about 0.14
relative to fiducial SN Type Ia. The distance turned out to be 31.0 pm 3 Mpc.
In addition, the heavily obscured SN 2002cv was also detected on the I frame
taken on JD 2452434 (June 8, 2002), and a variable star is found in the field,
very close to the host galaxy.Comment: accepted by Astronomy and Astrophysic
Effect of Long-Term Cycling Load for Abutment Screw Fixation in Implant Prosthodontics
The aim of this in vitro study was to use rotational tests on commercially available abutment screws to evaluate their potential for preload generation and to follow changes in torque by using newer fixation geometry on the interface of the implant-abutment screw joint. Five identical implant/abutment assemblies were chosen from each of the following systems: external hex with standard abutment and Replace with TorgTite screw (Nobel Biocare), Camlog universal abutment (Altatec Biotechnologies), DenTi internal hex (Dentimplant Ltd. Szentes, Hungary), straight abutment with internal antirotational element (Uniplant, Sinalisal, Budapest). Wax patterns of the upper premolar were performed and then cast from nickel-chrome alloy and full crown castings were cemented on abutments. In a test machine the magnitude and time of chewing function was predefined by using the desired force pattern. Each specimen
was stressed for cycles equivalent to an intaoral load of 5 months or longer timescale. In the static test greater loss in torques was calculated for standard Branemark and Replace screw joints.
Assuming that the optimum proportion is the same when we calculate loosening versus tightening torque we obtained a decrease between 0.70-0.59 for Replace and Branemark abutments and a more moderate loss of between 0.90-0.84 for the other systems investigated. The ten month equivalent cycling test produced a loosening torque of 16-17 Ncm for Branemark and Replace abutments. Similar decrease in torque was not found for the
other three systems. It was concluded that different approach in achievement of necessary mechanical integration can be seen in implant systems, although a reliable loosening torque could be measured after a longer time scale
Effect of Long-Term Cycling Load for Abutment Screw Fixation in Implant Prosthodontics
The aim of this in vitro study was to use rotational tests on commercially available abutment screws to evaluate their potential for preload generation and to follow changes in torque by using newer fixation geometry on the interface of the implant-abutment screw joint. Five identical implant/abutment assemblies were chosen from each of the following systems: external hex with standard abutment and Replace with TorgTite screw (Nobel Biocare), Camlog universal abutment (Altatec Biotechnologies), DenTi internal hex (Dentimplant Ltd. Szentes, Hungary), straight abutment with internal antirotational element (Uniplant, Sinalisal, Budapest). Wax patterns of the upper premolar were performed and then cast from nickel-chrome alloy and full crown castings were cemented on abutments. In a test machine the magnitude and time of chewing function was predefined by using the desired force pattern. Each specimen
was stressed for cycles equivalent to an intaoral load of 5 months or longer timescale. In the static test greater loss in torques was calculated for standard Branemark and Replace screw joints.
Assuming that the optimum proportion is the same when we calculate loosening versus tightening torque we obtained a decrease between 0.70-0.59 for Replace and Branemark abutments and a more moderate loss of between 0.90-0.84 for the other systems investigated. The ten month equivalent cycling test produced a loosening torque of 16-17 Ncm for Branemark and Replace abutments. Similar decrease in torque was not found for the
other three systems. It was concluded that different approach in achievement of necessary mechanical integration can be seen in implant systems, although a reliable loosening torque could be measured after a longer time scale
The Properties of Jovian Trojan Asteroids Listed in SDSS Moving Object Catalog 3
We analyze 1187 observations of about 860 unique candidate Jovian Trojan
asteroids listed in the 3rd release of Sloan Digital Sky Survey (SDSS) Moving
Object Catalog. The sample is complete at the faint end to r=21.2 mag (apparent
brightness) and H=13.8 (absolute brightness, approximately corresponding to 10
km diameter). A subset of 297 detections of previously known Trojans were used
to design and optimize a selection method based on observed angular velocity
that resulted in the remaining objects. Using a sample of objects with known
orbits, we estimate that the candidate sample contamination is about 3%. The
well-controlled selection effects, the sample size, depth and accurate
five-band UV-IR photometry enabled several new findings and the placement of
older results on a firmer statistical footing. We find that there are
significantly more asteroids in the leading swarm (L4) than in the trailing
swarm (L5): N(L4)/N(L5)=1.60.1, independently of limiting object's size.
The overall counts normalization suggests that there are about as many Jovians
Trojans as there are main-belt asteroids down to the same size limit, in
agreement with earlier estimates. We find that Trojan asteroids have a
remarkably narrow color distribution (root-mean-scatter of only 0.05 mag)
that is significantly different from the color distribution of the main-belt
asteroids. The color of Trojan asteroids is correlated with their orbital
inclination, in a similar way for both swarms, but appears uncorrelated with
the object's size. We extrapolate the results presented here and estimate that
Large Synoptic Survey Telescope will determine orbits, accurate colors and
measure light curves in six photometric bandpasses for about 100,000 Jovian
Trojan asteroids.Comment: 17 pages, 19 figures (49 figure panels), 1 table, accepted by MNRA
Multiperiodicity in semiregular variables II. Systematic amplitude variations
We present a detailed lightcurve analysis for a sample of bright semiregular
variables based on long-term (70--90 years) visual magnitude estimates carried
out by amateur astronomers. Fundamental changes of the physical state
(amplitude and/or frequency modulations, mode change and switching) are studied
with the conventional Fourier- and wavelet analysis.
The light curve of the carbon Mira Y Per showing a gradual amplitude decrease
has been re-analysed after collecting and adding current data to earlier ones.
The time scales of the sudden change and convection are compared and their
similar order of magnitude is interpreted to be a possible hint for strong
coupling between pulsation and convection. The periods of the biperiodic
low-amplitude light curve and their ratios suggest a pulsation in the first and
third overtone modes. An alternative explanation of the observed behaviour
could be a period halving due to the presence of weak chaos.
Beside two examples of repetitive mode changes (AF Cyg and W Cyg) we report
three stars with significant amplitude modulations (RY Leo, RX UMa and RY UMa).
A simple geometric model of a rotationally induced amplitude modulation in RY
UMa is outlined assuming low-order nonradial oscillation, while the observed
behaviour of RX UMa and RY Leo is explained as a beating of two closely
separated modes of pulsation. This phenomenon is detected unambiguously in V
CVn, too. The period ratios found in these stars (1.03-1.10) suggest either
high-order overtone or radial+non-radial oscillation.Comment: 11 pages + 17 figures, accepted for publication in A&A Supplement
Serie
Activity of 50 Long-Period Comets Beyond 5.2 AU
Remote investigations of the ancient solar system matter has been
traditionally carried out through the observations of long-period (LP) comets
that are less affected by solar irradiation than the short-period counterparts
orbiting much closer to the Sun. Here we summarize the results of our
decade-long survey of the distant activity of LP comets. We found that the most
important separation in the dataset is based on the dynamical nature of the
objects. Dynamically new comets are characterized by a higher level of activity
on average: the most active new comets in our sample can be characterized by
afrho values >3--4 higher than that of our most active returning comets. New
comets develop more symmetric comae, suggesting a generally isotropic outflow.
Contrary to this, the coma of recurrent comets can be less symmetrical,
ocassionally exhibiting negative slope parameters, suggesting sudden variations
in matter production. The morphological appearance of the observed comets is
rather diverse. A surprisingly large fraction of the comets have long, teniouos
tails, but the presence of impressive tails does not show a clear correlation
with the brightness of the comets.Comment: 21 pages, 4 figures, accepted for publication in A
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