152 research outputs found
A Pseudo DNA Cryptography Method
The DNA cryptography is a new and very promising direction in cryptography
research. DNA can be used in cryptography for storing and transmitting the
information, as well as for computation. Although in its primitive stage, DNA
cryptography is shown to be very effective. Currently, several DNA computing
algorithms are proposed for quite some cryptography, cryptanalysis and
steganography problems, and they are very powerful in these areas. However, the
use of the DNA as a means of cryptography has high tech lab requirements and
computational limitations, as well as the labor intensive extrapolation means
so far. These make the efficient use of DNA cryptography difficult in the
security world now. Therefore, more theoretical analysis should be performed
before its real applications.
In this project, We do not intended to utilize real DNA to perform the
cryptography process; rather, We will introduce a new cryptography method based
on central dogma of molecular biology. Since this method simulates some
critical processes in central dogma, it is a pseudo DNA cryptography method.
The theoretical analysis and experiments show this method to be efficient in
computation, storage and transmission; and it is very powerful against certain
attacks. Thus, this method can be of many uses in cryptography, such as an
enhancement insecurity and speed to the other cryptography methods. There are
also extensions and variations to this method, which have enhanced security,
effectiveness and applicability.Comment: A small work that quite some people asked abou
Chiral patterns arising from electrostatic growth models
Recently, unusual and strikingly beautiful seahorse-like growth patterns have
been observed under conditions of quasi-two-dimensional growth. These
`S'-shaped patterns strongly break two-dimensional inversion symmetry; however
such broken symmetry occurs only at the level of overall morphology, as the
clusters are formed from achiral molecules with an achiral unit cell. Here we
describe a mechanism which gives rise to chiral growth morphologies without
invoking microscopic chirality. This mechanism involves trapped electrostatic
charge on the growing cluster, and the enhancement of growth in regions of
large electric field. We illustrate the mechanism with a tree growth model,
with a continuum model for the motion of the one-dimensional boundary, and with
microscopic Monte Carlo simulations. Our most dramatic results are found using
the continuum model, which strongly exhibits spontaneous chiral symmetry
breaking, and in particular finned `S' shapes like those seen in the
experiments.Comment: RevTeX, 12 pages, 9 figure
Spatially resolved Spectro-photometry of M81: Age, Metallicity and Reddening Maps
In this paper, we present a multi-color photometric study of the nearby
spiral galaxy M81, using images obtained with the Beijing Astronomical
Observatory 60/90 cm Schmidt Telescope in 13 intermediate-band filters from
3800 to 10000{\AA}. The observations cover the whole area of M81 with a total
integration of 51 hours from February 1995 to February 1997. This provides a
multi-color map of M81 in pixels of 1\arcsec.7 \times 1\arcsec.7. Using
theoretical stellar population synthesis models, we demonstrate that some BATC
colors and color indices can be used to disentangle the age and metallicity
effect. We compare in detail the observed properties of M81 with the
predictions from population synthesis models and quantify the relative chemical
abundance, age and reddening distributions for different components of M81. We
find that the metallicity of M81 is about with no significant
difference over the whole galaxy. In contrast, an age gradient is found between
stellar populations of the central regions and of the bulge and disk regions of
M81: the stellar population in its central regions is older than 8 Gyr while
the disk stars are considerably younger, Gyr. We also give the
reddening distribution in M81. Some dust lanes are found in the galaxy bulge
region and the reddening in the outer disk is higher than that in the central
regions.Comment: Accepted for publication in AJ (May 2000 issue). 27 pages including 6
figures. Uses AASTeX aasms4 styl
Intermediate-band Surface Photometry of the Edge-on Galaxy: NGC 4565
We present a deep, 42.79 hr image of the nearby, edge-on galaxy NGC 4565 in
the
Beijing-Arizona-Taipei-Connecticut (BATC) 6660A band using the large-format
CCD system on the 0.6m Schmidt telescope at the Xinglong Station of the
National
Astronomical Observatories of China (NAOC). we obtain a final image that is
calibrated to an accuracy of 0.02 mag in zero point, and for which we can
measure galaxy surface brightness to an accuracy of 0.25 mag at a surface
brightness at 27.5 mag arcsec^-2 at 6660A, corresponding to a distance of 22
kpc from the center of the disk. The integrated magnitude of NGC4565 in our
filter is m6660=8.99 (R magnitude of 9.1) to a surface brightness of 28 mag
arcsec-2. We analyze the faint outer parts of this galaxy using a
two-dimensional model comprised of three components: an exponential thin disk,
an exponential thick disk, and a power-law halo. A total of 12 parameters are
included in our model. We determine the best values of our model parameters via
10,000 random initial values, 3,700 of which converge to final values. The thin
disk and thick disk parameters we determine here are consistent with those of
previous studies of this galaxy. However, our very deep image permits a better
determination of the power law fit to the halo, constraining this power law to
be between r^-3.2 and r^-4.0, with a best fit value of r^-3.88. We find the
axis ratio of the halo to be 0.44 and its core radius to be 14.4 kpc (for an
adopted distance of 14.5 Mpc).Comment: 34 pages, 11 figures, will appear in March 2002 of A
Infant Brain Atlases from Neonates to 1- and 2-Year-Olds
Background: Studies for infants are usually hindered by the insufficient image contrast, especially for neonates. Prior knowledge, in the form of atlas, can provide additional guidance for the data processing such as spatial normalization, label propagation, and tissue segmentation. Although it is highly desired, there is currently no such infant atlas which caters for all these applications. The reason may be largely due to the dramatic early brain development, image processing difficulties, and the need of a large sample size. Methodology: To this end, after several years of subject recruitment and data acquisition, we have collected a unique longitudinal dataset, involving 95 normal infants (56 males and 39 females) with MRI scanned at 3 ages, i.e., neonate, 1-yearold, and 2-year-old. State-of-the-art MR image segmentation and registration techniques were employed, to construct which include the templates (grayscale average images), tissue probability maps (TPMs), and brain parcellation maps (i.e., meaningful anatomical regions of interest) for each age group. In addition, the longitudinal correspondences between agespecific atlases were also obtained. Experiments of typical infant applications validated that the proposed atlas outperformed other atlases and is hence very useful for infant-related studies. Conclusions: We expect that the proposed infant 0–1–2 brain atlases would be significantly conducive to structural and functional studies of the infant brains. These atlases are publicly available in our website
Cerebrospinal fluid oligoclonal bands in Chinese patients with multiple sclerosis: the prevalence and its association with clinical features
BackgroundCerebrospinal fluid oligoclonal band (CSF-OCB) is an established biomarker in diagnosing multiple sclerosis (MS), however, there are no nationwide data on CSF-OCB prevalence and its diagnostic performance in Chinese MS patients, especially in the virtue of common standard operation procedure (SOP).MethodsWith a consensus SOP and the same isoelectric focusing system, we conducted a nationwide multi-center study on OCB status in consecutively, and recruited 483 MS patients and 880 non-MS patients, including neuro-inflammatory diseases (NID, n = 595) and non-inflammatory neurological diseases (NIND, n=285). Using a standardized case report form (CRF) to collect the clinical, radiological, immunological, and CSF data, we explored the association of CSF-OCB positivity with patient characters and the diagnostic performance of CSF-OCB in Chinese MS patients. Prospective source data collection, and retrospective data acquisition and statistical data analysis were used.Findings369 (76.4%) MS patients were OCB-positive, while 109 NID patients (18.3%) and 6 NIND patients (2.1%) were OCB-positive, respectively. Time from symptom onset to diagnosis was significantly shorter in OCB-positive than that in OCB-negative MS patients (13.2 vs 23.7 months, P=0.020). The prevalence of CSF-OCB in Chinese MS patients was significantly higher in high-latitude regions (41°-50°N)(P=0.016), and at high altitudes (>1000m)(P=0.025). The diagnostic performance of CSF-OCB differentiating MS from non-MS patients yielded a sensitivity of 76%, a specificity of 87%.InterpretationThe nationwide prevalence of CSF-OCB was 76.4% in Chinese MS patients, and demonstrated a good diagnostic performance in differentiating MS from other CNS diseases. The CSF-OCB prevalence showed a correlation with high latitude and altitude in Chinese MS patients
A novel noise assessment method based on human core competency
The tough noise environment in helicopter cockpit can passively influence pilots in mental and physical way, weaken their core competency, and as a result, maybe causing pilot error and even accidents. The current research can evaluate the physical characteristics of noise and its impact on emotion such as noise annoyance, but it ignores the impact of cockpit noise on human competence. Therefore, this paper establishes a noise evaluation and prediction model based on core competence with task performance, cognitive load and eye movement data. Experiment is designed and implemented in three noise levels and three task difficulties to verify the model. The results indicate that: 1) core competency and task accuracy decline in higher noise levels significantly. 2) the noise assessment method based on core competency can accurately predict the influence of noise on human performance. This novel method can quantitatively reflect the impact of noise changes on human performance in emergency condition. It can expand the connotation of noise evaluation, provide the evaluation and control of cockpit noise with theoretical explanations, and provide the optimization design of helicopter cockpit with practical data
Research on the Applicability of Touchscreens in Manned/Unmanned Aerial Vehicle Cooperative Missions
The suitability of touchscreens for human–computer interaction in manned/unmanned aerial vehicle cooperative missions remains uncertain, especially in situations that are time-sensitive with variations in difficulty levels. The purpose of this study is to determine the feasibility of touchscreen applications in manned/unmanned aerial vehicle cooperative missions and the magnitude of the effects of time pressure and task difficulty. In contrast to previous studies, a combination of performance and perceptual load measures was used to divide errors into disposition errors, undetected errors, and miscalculation errors to explore specific error mechanisms, set up typical manned/unmanned aerial vehicle cooperative human–computer interaction tasks, and set up antecedent features for potential factors. Thirty subjects participated in an experiment that required the use of touchscreens or keyboards to perform a human–computer interaction task in a simulated manned/unmanned aerial vehicle cooperative mission. Experiments were set at three task difficulties: low, medium, and high, and were matched to a set time pressure or no time pressure for two seconds for low difficulty, three seconds for medium difficulty, and four seconds for high difficulty. The results showed that the touchscreens improved the participants’ response speed at a time pressure of 2 s or less compared with the use of a general input device; however, the task error rate also increased significantly. The higher the task difficulty was, the worse the performance was and the greater the perceived workload of the participants. The application of touchscreens in dynamic environments subjected the participants to greater physical demands. The performance of participants using a keyboard was no better than that when touchscreens were used during the experiment. Moreover, touchscreens did not significantly improve participant performance. The results support the possibility of using touchscreens in manned/unmanned aerial vehicle cooperative missions
STRUCTURE DYNAMIC CHARACTER OPTIMIZATION AT THERMAL ENVIRONMENT
Many aircraft structures are in thermal and vibration composite environment,and the two both should be taken into account in structural optimization design. Thermal environment influences the structural dynamic characteristics on the change of structural stiffness matrix,and then changes of the structure natural frequency. Basing on the analysis of structural dynamics in thermal environment optimization model was built both for uniform temperature field and thermal conduction structure Considering the manufacture process, the model optimizes the dynamic characteristics of structure. Results suggest that optimization considering the thermal environment of structural dynamics characteristics can improve the structure natural frequency and then keep the natural frequency away from the range of external excitation frequency to avoid resonance phenomenon caused by the change of the structural natural frequency resulting in thermal environment
An Enriched Finite Element Method with Appropriate Interpolation Cover Functions for Transient Wave Propagation Dynamic Problems
A novel enriched finite element method (EFEM) was employed to analyze the transient wave propagation problems. In the present method, the traditional finite element approximation was enriched by employing the appropriate interpolation covers. We mathematically and numerically showed that the present EFEM possessed the important monotonic convergence property with the decrease of the used time steps for transient wave propagation problems when the unconditional stable Newmark time integration scheme was used for time integration. This attractive property markedly distinguishes the present EFEM from the traditional FEM for transient wave propagation problems. Two typical numerical examples were given to demonstrate the capabilities of the present method
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