10,789 research outputs found
Quaternions and Special Relativity
We reformulate Special Relativity by a quaternionic algebra on reals. Using
{\em real linear quaternions}, we show that previous difficulties, concerning
the appropriate transformations on the space-time, may be overcome. This
implies that a complexified quaternionic version of Special Relativity is a
choice and not a necessity.Comment: 17 pages, latex, no figure
Shedding Light on Diatom Photonics by means of Digital Holography
Diatoms are among the dominant phytoplankters in the worl's ocean, and their
external silica investments, resembling artificial photonics crystal, are
expected to play an active role in light manipulation. Digital holography
allowed studying the interaction with light of Coscinodiscus wailesii cell wall
reconstructing the light confinement inside the cell cytoplasm, condition that
is hardly accessible via standard microscopy. The full characterization of the
propagated beam, in terms of quantitative phase and intensity, removed a
long-standing ambiguity about the origin of the light. The data were discussed
in the light of living cell behavior in response to their environment
An Observational Cohort Study on Delayed-Onset Infections after Mandibular Third-Molar Extractions.
OBJECTIVES:
The purpose of the present study was to investigate the occurrence and clinical features of delayed-onset infections after mandibular third-molar extractions.
METHOD AND MATERIALS:
An observational cohort study was conducted on 179 patients undergoing mandibular third-molar extraction between January 2013 and December 2015, for a total of 217 extractions. Data were recorded at the time of extraction (T0), on suture removal seven days later (T1), and 30 days after the extraction, when patients were contacted and asked about their healing process (T2). The statistical analysis was performed with nonparametric tests. A p value lower than 0.05 was considered statistically significant.
RESULTS:
Eight delayed-onset infections were recorded, amounting to 3.7% of all extractions. The median time elapsing from the extraction to the delayed-onset infection was 35 days (IQR 28-40; min 24-max 49). Younger age and longer surgical procedures seemed to be more often associated with this complication.
CONCLUSION:
Delayed-onset infections after third-molar extractions are relatively rare postoperative complications characterized by a swelling, usually with a purulent discharge. Patients should be informed of this possibility, which might develop even several weeks after the extraction
Axial dependence of optical weak measurements in the critical region
The interference between optical beams of different polarizations plays a
fundamental role in reproducing the optical analog of the electron spin weak
measurement. The extraordinary point in optical weak measurements is
represented by the possibility to estimate with great accuracy the
Goos-Haenchen (GH) shift by measuring the distance between the peak of the
outgoing beams for two opposite rotation angles of the polarizers located
before and after the dielectric block. Starting from the numerical calculation
of the GH shift, which clearly shows a frequency crossover for incidence near
to the critical angle, we present a detailed study of the interference between
s and p polarized waves in the critical region. This allows to determine in
which conditions it is possible to avoid axial deformations and reproduce the
GH curves. In view of a possible experimental implementation, we give the
expected weak measurement curves for Gaussian lasers of different beam waist
sizes propagating through borosilicate (BK7) and fused silica dielectric
blocks.Comment: 16 pages, 7 figure
Octonionic Representations of GL(8,R) and GL(4,C)
Octonionic algebra being nonassociative is difficult to manipulate. We
introduce left-right octonionic barred operators which enable us to reproduce
the associative GL(8,R) group. Extracting the basis of GL(4,C), we establish an
interesting connection between the structure of left-right octonionic barred
operators and generic 4x4 complex matrices. As an application we give an
octonionic representation of the 4-dimensional Clifford algebra.Comment: 14 pages, Revtex, J. Math. Phys. (submitted
Bulk and surface biaxiality in nematic liquid crystals
Nematic liquid crystals possess three different phases: isotropic, uniaxial,
and biaxial. The ground state of most nematics is either isotropic or uniaxial,
depending on the external temperature. Nevertheless, biaxial domains have been
frequently identified, especially close to defects or external surfaces. In
this paper we show that any spatially-varying director pattern may be a source
of biaxiality. We prove that biaxiality arises naturally whenever the symmetric
tensor \Sb=(\grad \nn)(\grad \nn)^T possesses two distinct nonzero
eigenvalues. The eigenvalue difference may be used as a measure of the expected
biaxiality. Furthermore, the corresponding eigenvectors indicate the directions
in which the order tensor \QQ is induced to break the uniaxial symmetry about
the director \nn. We apply our general considerations to some examples. In
particular we show that, when we enforce homeotropic anchoring on a curved
surface, the order tensor become biaxial along the principal directions of the
surface. The effect is triggered by the difference in surface principal
curvatures
TE Wave Measurement and Modeling
In the TE wave method, microwaves are coupled into the beam-pipe and the
effect of the electron cloud on these microwaves is measured. An electron cloud
(EC) density can then be calculated from this measurement. There are two
analysis methods currently in use. The first treats the microwaves as being
transmitted from one point to another in the accelerator. The second more
recent method, treats the beam-pipe as a resonant cavity. This paper will
summarize the reasons for adopting the resonant TE wave analysis as well as
give examples from CESRTA and DA{\Phi}NE of resonant beam-pipe. The results of
bead-pull bench measurements will show some possible standing wave patterns,
including a cutoff mode (evanescent) where the field decreases exponentially
with distance from the drive point. We will outline other recent developments
in the TE wave method including VORPAL simulations of microwave resonances, as
well as the simulation of transmission in the presence of both an electron
cloud and magnetic fields.Comment: Presented at ECLOUD'12: Joint INFN-CERN-EuCARD-AccNet Workshop on
Electron-Cloud Effects, La Biodola, Isola d'Elba, Italy, 5-9 June 2012;
CERN-2013-002, pp. 193-20
- …