212 research outputs found
Losing money with a high Sharpe ratio
A simple example shows that losing all money is compatible with a very high
Sharpe ratio (as computed after losing all money). However, the only way that
the Sharpe ratio can be high while losing money is that there is a period in
which all or almost all money is lost. This note explores the best achievable
Sharpe and Sortino ratios for investors who lose money but whose one-period
returns are bounded below (or both below and above) by a known constant.Comment: 6 page
Scale distributions and fractal dimensions in turbulence
A new geometric framework connecting scale distributions to coverage statistics is employed to analyze level sets arising in turbulence as well as in other phenomena. A 1D formalism is described and applied to Poisson, lognormal, and power-law statistics. A d-dimensional generalization is also presented. Level sets of 2D spatial measurements of jet-fluid concentration in turbulent jets are analyzed to compute scale distributions and fractal dimensions. Lognormal statistics are used to model the level sets at inner scales. The results are in accord with data from other turbulent flows
Murray Gell-Mann, A Short Appreciation
On September 25, 2014 Murray Gell-Mann was presented with the Helmholz Medal
of the Berlin Brandenburg Academy of Sciences and Humanities in a ceremony at
the Santa Fe Institute. The author, among others, was asked to speak for
fifteen minutes on Murray and his accomplishments. The following is an edited
transcription of the author's speaking text.Comment: 6 pages, revtex, picture added, typos fixe
No Time Asymmetry from Quantum Mechanics
With CPT-invariant initial conditions that commute with CPT-invariant final
conditions, the respective probabilities (when defined) of a set of histories
and its CPT reverse are equal, giving a CPT-symmetric universe. This leads me
to question whether the asymmetry of the Gell-Mann--Hartle decoherence
functional for ordinary quantum mechanics should be interpreted as an asymmetry
of {\it time} .Comment: 14 pages, Alberta-Thy-11-9
Improvement of mouth functional disability in systemic sclerosis patients over one year in a trial of fat transplantation versus adipose-derived stromal cells
Background. Systemic sclerosis (SSc) is a multisystem disease characterized by cutaneous and visceral fibrosis. Face and mouth changes include telangiectasia, sicca syndrome, and thinning and reduction of mouth width (microcheilia) and opening (microstomia). We applied autologous fat transplantation compared with autologous adipose-derived stromal cells (ADSCs) injection to evaluate the clinical improvement of mouth opening. Methods. From February to May 2013 ten consecutive SSc patients were enrolled from the outpatient clinic of Plastic Surgery Department of Sapienza University of Rome. Patients were divided into two groups as follows: 5 patients were treated with fat transplantation and 5 patients received infiltration of ADSCs produced by cell factory of our institution. To value mouth opening, we use the Italian version of Mouth Handicap in Systemic Sclerosis Scale (IvMHISS). Mouth opening was assessed in centimetres (Maximal Mouth Opening, MMO). In order to evaluate compliance and physician and patient satisfaction, we employed a Questionnaire of Satisfaction and the Visual Analogic Scale (VAS) performed before starting study and 1 year after the last treatment. Results and Conclusion. We noticed that both procedures obtained significant results but neither one emerged as a first-choice technique. The present clinical experimentation should be regarded as a starting point for further experimental research and clinical trials
A laser-induced heat flux technique for convective heat transfer measurements in high speed flows
A technique is developed to measure the local convective heat transfer coefficient on a model surface in a supersonic flow field. The technique uses a laser to apply a discrete local heat flux at the model test surface, and an infrared camera system determines the local temperature distribution due to the heating. From this temperature distribution and an analysis of the heating process, a local convective heat transfer coefficient is determined. The technique was used to measure the local surface convective heat transfer coefficient distribution on a flat plate at nominal Mach numbers of 2.5, 3.0, 3.5, and 4.0. The flat plate boundary layer initially was laminar and became transitional in the measurement region. The experimentally determined convective heat transfer coefficients were generally higher than the theoretical predictions for flat plate laminar boundary layers. However, the results indicate that this nonintrusive optical measurement technique has the potential to measure surface convective heat transfer coefficients in high speed flow fields
Monolithically integrated InAsSb-based nBnBn heterostructure on GaAs for infrared detection
High operating temperature i
nfrared
photo
detectors
with multi
-color function
that are
capable of monolithic
integration
are of increasing importance
in developing the next
generation
of
mid
-IR
imag
e sensors.
Applications of these sensors
include defense, medical diagnosis, environmental and
astronomical observations.
We
have
investigated a novel
InAsSb
-based nBnBn heterostructure that combines a state
-of-art
InAsSb nBn detector with
an
InAsSb/GaSb heterojuncti
on
detector
. At room temperature, r
educti
on
in the dark current
density of more than an order of magnitude
was
achieved
compared to
previously investigated
InAsSb/GaSb heterojunction
dete
ctors
.
Electrical
characterization
from
cryogenic
temperatures to roo
m temperature
confirmed that the nBnBn
device was diffusion limited
for temperature
s above 150K. O
ptical
measurements
demonstrated that the
nBnBn detector
was
sensitive in
both
the
SWIR and MWIR wavelength range at
room
temperature
. The specific
detectivity
(D*)
of the competed nBnBn
devices
was calculated to be
8.6
×
10
8
cm
·
Hz
1/2
W
-1
at 300K and
approximately 1.0
×
10
10
cm
·
Hz
1/2
W
-1
when cooled down to 200K
(with
0.3V reverse bias
and 1550nm illumination
). In addition,
all
photodetector layers were
grown monolithically on GaAs active
layers u
sing the interfacial misfit
array
growth
mode
. Our results
therefore pave the way
for the development of
new active pixel
designs for monolithically integrated mid
-IR imaging arrays
- …