2,530 research outputs found
Z_3 Symmetry and Neutrino Mixing in Type II Seesaw
Neutrino mixing matrix satisfying the current experimental data can be well
described by the HPS tri-bimaximal mixing matrix. We propose that its origin
can be understood within the seesaw framework by a hidden condition on the mass
matrix of heavy right-handed neutrinos under the transformation of the Abelian
finite group Z_3 on the flavor basis. Ignoring CP phases, we show that it can
lead to the generic form of the effective light neutrino mass matrix from which
the HPS mixing matrix appears naturally, as well as an expeimentally allowed
non-zero \sin\theta_{13}. We show that the model based on our proposal is in
good agreement with the current experimental data.Comment: 9 page
A Simple Method to Estimate the Time-dependent ROC Curve Under Right Censoring
The time-dependent Receiver Operating Characteristic (ROC) curve is often used to study the diagnostic accuracy of a single continuous biomarker, measured at baseline, on the onset of a disease condition when the disease onset may occur at different times during the follow-up and hence may be right censored. Due to censoring, the true disease onset status prior to the pre-specified time horizon may be unknown on some patients, which causes difficulty in calculating the time-dependent sensitivity and specificity. We study a simple method that adjusts for censoring by weighting the censored data by the conditional probability of disease onset prior to the time horizon given the biomarker and the observed censoring time. Our numerical study shows that the proposed method produces unbiased and efficient estimators of time-dependent sensitivity and specificity as well as area under the ROC curve, and outperforms several other published methods currently implemented in R packages
Can virtual reality predict body part discomfort and performance of people in realistic world for assembling tasks?
This paper presents our work on relationship of evaluation results between
virtual environment (VE) and realistic environment (RE) for assembling tasks.
Evaluation results consist of subjective results (BPD and RPE) and objective
results (posture and physical performance). Same tasks were performed with same
experimental configurations and evaluation results were measured in RE and VE
respectively. Then these evaluation results were compared. Slight difference of
posture between VE and RE was found but not great difference of effect on
people according to conventional ergonomics posture assessment method.
Correlation of BPD and performance results between VE and RE are found by
linear regression method. Moreover, results of BPD, physical performance, and
RPE in VE are higher than that in RE with significant difference. Furthermore,
these results indicates that subjects feel more discomfort and fatigue in VE
than RE because of additional effort required in VE
A novel approach for determining fatigue resistances of different muscle groups in static cases
In ergonomics and biomechanics, muscle fatigue models based on maximum
endurance time (MET) models are often used to integrate fatigue effect into
ergonomic and biomechanical application. However, due to the empirical
principle of those MET models, the disadvantages of this method are: 1) the MET
models cannot reveal the muscle physiology background very well; 2) there is no
general formation for those MET models to predict MET. In this paper, a
theoretical MET model is extended from a simple muscle fatigue model with
consideration of the external load and maximum voluntary contraction in passive
static exertion cases. The universal availability of the extended MET model is
analyzed in comparison to 24 existing empirical MET models. Using mathematical
regression method, 21 of the 24 MET models have intraclass correlations over
0.9, which means the extended MET model could replace the existing MET models
in a general and computationally efficient way. In addition, an important
parameter, fatigability (or fatigue resistance) of different muscle groups,
could be calculated via the mathematical regression approach. Its mean value
and its standard deviation are useful for predicting MET values of a given
population during static operations. The possible reasons influencing the
fatigue resistance were classified and discussed, and it is still a very
challenging work to find out the quantitative relationship between the fatigue
resistance and the influencing factors
Hawking radiation-quasinormal modes correspondence for large AdS black holes
It is well-known that the non-strictly thermal character of the Hawking
radiation spectrum generates a natural correspondence between Hawking radiation
and black hole quasinormal modes. This main issue has been analyzed in the
framework of Schwarzschild black holes, Kerr black holes and nonextremal
Reissner-Nordstrom black holes. In this paper, by introducing the effective
temperature, we reanalysis the non-strictly thermal character of large AdS
black holes. The results show that the effective mass corresponding to the
effective temperature is approximatively the average one in any dimension. And
the other effective quantities can also be obtained. Based on the known forms
of frequency in quasinormal modes, we reanalysis the asymptotic frequencies of
the large AdS black hole in three and five dimensions. Then we get the formulas
of the Bekenstein-Hawking entropy and the horizon's area quantization with
functions of the quantum "overtone" number .Comment: 6 page
Formation of drying crack patterns in soils: a deterministic approach
Soils, as well as most of deformable multiphase porous materials, are likely to suffer from desiccation cracking, leading to the formation of regular crack patterns affecting their permeability. The ensuing crack spacing has often been related to a concept sometimes called "sequential infilling”: it is assumed that desiccation cracks are formed by successive generations. However, such a concept does not consider the pattern of a simultaneous crack formation at a given moment. Using our desiccation cracking test results and their numerical simulation, we propose a consistent explanation for the formation of desiccation crack patterns in soils. We show that the "sequential infilling” concept is suitable only when the position of the crack(s) clearly stems from the stress field. To derive an estimate of the desiccation crack spacing, the overall energy of the system needs to be considered. Statistical variability should be superimposed on the mean deterministic conditions discussed her
Integrating digital human modeling into virtual environment for ergonomic oriented design
International audienceVirtual human simulation integrated into virtual reality applications is mainly used for virtual representation of the user in virtual environment or for interactions between the user and the virtual avatar for cognitive tasks. In this paper, in order to prevent musculoskeletal disorders, the integration of virtual human simulation and VR application is presented to facilitate physical ergonomic evaluation, especially for physical fatigue evaluation of a given population. Immersive working environments are created to avoid expensive physical mock-up in conventional evaluation methods. Peripheral motion capture systems are used to capture natural movements and then to simulate the physical operations in virtual human simulation. Physical aspects of human's movement are then analyzed to determine the effort level of each key joint using inverse kinematics. The physical fatigue level of each joint is further analyzed by integrating a fatigue and recovery model on the basis of physical task parameters. All the process has been realized based on VRHIT platform and a case study is presented to demonstrate the function of the physical fatigue for a given population and its usefulness for worker selection
PLGA-based gene delivering nanoparticle enhance suppression effect of miRNA in HePG2 cells
The biggest challenge in the field of gene therapy is how to effectively deliver target genes to special cells. This study aimed to develop a new type of poly(D,L-lactide-co-glycolide) (PLGA)-based nanoparticles for gene delivery, which are capable of overcoming the disadvantages of polyethylenimine (PEI)- or cationic liposome-based gene carrier, such as the cytotoxicity induced by excess positive charge, as well as the aggregation on the cell surface. The PLGA-based nanoparticles presented in this study were synthesized by emulsion evaporation method and characterized by transmission electron microscopy, dynamic light scattering, and energy dispersive spectroscopy. The size of PLGA/PEI nanoparticles in phosphate-buffered saline (PBS) was about 60 nm at the optimal charge ratio. Without observable aggregation, the nanoparticles showed a better monodispersity. The PLGA-based nanoparticles were used as vector carrier for miRNA transfection in HepG2 cells. It exhibited a higher transfection efficiency and lower cytotoxicity in HepG2 cells compared to the PEI/DNA complex. The N/P ratio (ratio of the polymer nitrogen to the DNA phosphate) 6 of the PLGA/PEI/DNA nanocomplex displays the best property among various N/P proportions, yielding similar transfection efficiency when compared to Lipofectamine/DNA lipoplexes. Moreover, nanocomplex shows better serum compatibility than commercial liposome. PLGA nanocomplexes obviously accumulate in tumor cells after transfection, which indicate that the complexes contribute to cellular uptake of pDNA and pronouncedly enhance the treatment effect of miR-26a by inducing cell cycle arrest. Therefore, these results demonstrate that PLGA/PEI nanoparticles are promising non-viral vectors for gene delivery
Mid-infrared computational temporal ghost imaging
Ghost imaging in the time domain allows for reconstructing fast temporal
objects using a slow photodetector. The technique involves correlating random
or pre-programmed probing temporal intensity patterns with the integrated
signal measured after modulation by the temporal object. However, the
implementation of temporal ghost imaging necessitates ultrafast detectors or
modulators for measuring or pre-programming the probing intensity patterns,
which is not universally available in all spectral regions especially in the
mid-infrared range. Here, we demonstrate a frequency downconversion temporal
ghost imaging scheme that enables to extend the operation regime to arbitrary
wavelengths regions where fast modulators and detectors are not available. The
approach modulates a signal with temporal intensity patterns in the
near-infrared and transfers the patterns to an idler via difference-frequency
generation at the wavelength of the temporal object to be retrieved. As a
proof-of-concept, we demonstrate temporal ghost imaging in the mid-infrared.
The scheme is flexible and introduces new possibilities for scan-free
pump-probe imaging and the study of ultrafast dynamics in spectral regions
where ultrafast modulation or detection is challenging such as the mid-infrared
and THz regions
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