Similarity Analysis of Projectile Penetration into Concrete

This paper presents a dimensionless model for the depth of penetration (DOP) of a projectile penetrating into a concrete target, based on the similarity theory involving intermediate asymptotics, complete similarity, and incomplete similarity. The calculated numerical results are in good agreement with previous experimental data, including two sets of full-scale and twenty-four sets of sub-scale penetration of non-deformable projectiles into concrete targets. Moreover, compared with several empirical and semi-empirical DOP models, the new model is applicable within a relatively broader range, including the penetration of both sub-scale and full-scale projectiles. For the limitations of the validity, dimensionless parameters Π3  = ϕt/ϕ larger than 12, Π4 = (ϕ3fc)/(Mv02) smaller than 0.1, and the initial impact velocity of the projectile less than about 900 to 1000m/s are necessary for the model

Rear-Surface Collapse of Finite Thickness Concrete Targets under Internal Explosion

An experimental investigation on the buried internal explosion in finite thickness concrete targets was carried out, with the aim at developing an available criterion for the critical collapse of rear-surface to determine the critical collapse thickness and the critical amount of explosive charge under different depth of buried. It is found, under a certain density and diameter of explosive charge, the critical collapse thickness increases monotonically with the length-to-diameter ratio or the amount of the explosive charge, but the increasing becomes slower down after the length-to-diameter ratio of the explosive charge is larger than about 5, which implies that the geometry of the explosive charge can have much influence on the damage and failure of concrete targets due to different mechanism of energy dissipation. Moreover, by using the dimensional analysis approach, the function relation between the dimensionless critical collapse thickness and the length-to-diameter ratio was obtained, which shows that the dimensionless critical collapse thickness depends on both the amount and the length-to-diameter ratio of the charge.Defence Science Journal, 2012, 62(5), pp.295-299, DOI:http://dx.doi.org/10.14429/dsj.62.123

Does or did the supernova remnant Cassiopeia A operate as a PeVatron?

For decades, supernova remnants (SNRs) have been considered the prime sources of Galactic Cosmic rays (CRs). But whether SNRs can accelerate CR protons to PeV energies and thus dominate CR flux up to the knee is currently under intensive theoretical and phenomenological debate. The direct test of the ability of SNRs to operate as CR PeVatrons can be provided by ultrahigh-energy (UHE; $E_\gamma \geq 100$~TeV) $\gamma$-rays. In this context, the historical SNR Cassiopeia A (Cas A) is considered one of the most promising target for UHE observations. This paper presents the observation of Cas A and its vicinity by the LHAASO KM2A detector. The exceptional sensitivity of LHAASO KM2A in the UHE band, combined with the young age of Cas A, enabled us to derive stringent model-independent limits on the energy budget of UHE protons and nuclei accelerated by Cas A at any epoch after the explosion. The results challenge the prevailing paradigm that Cas A-type SNRs are major suppliers of PeV CRs in the Milky Way.Comment: 11 pages, 3 figures, Accepted by the APJ

Measurement of ultra-high-energy diffuse gamma-ray emission of the Galactic plane from 10 TeV to 1 PeV with LHAASO-KM2A

The diffuse Galactic $\gamma$-ray emission, mainly produced via interactions between cosmic rays and the interstellar medium and/or radiation field, is a very important probe of the distribution, propagation, and interaction of cosmic rays in the Milky Way. In this work we report the measurements of diffuse $\gamma$-rays from the Galactic plane between 10 TeV and 1 PeV energies, with the square kilometer array of the Large High Altitude Air Shower Observatory (LHAASO). Diffuse emissions from the inner ($15^{\circ}<l<125^{\circ}$, $|b|<5^{\circ}$) and outer ($125^{\circ}<l<235^{\circ}$, $|b|<5^{\circ}$) Galactic plane are detected with $29.1\sigma$ and $12.7\sigma$ significance, respectively. The outer Galactic plane diffuse emission is detected for the first time in the very- to ultra-high-energy domain ($E>10$~TeV). The energy spectrum in the inner Galaxy regions can be described by a power-law function with an index of $-2.99\pm0.04$, which is different from the curved spectrum as expected from hadronic interactions between locally measured cosmic rays and the line-of-sight integrated gas content. Furthermore, the measured flux is higher by a factor of $\sim3$ than the prediction. A similar spectrum with an index of $-2.99\pm0.07$ is found in the outer Galaxy region, and the absolute flux for $10\lesssim E\lesssim60$ TeV is again higher than the prediction for hadronic cosmic ray interactions. The latitude distributions of the diffuse emission are consistent with the gas distribution, while the longitude distributions show clear deviation from the gas distribution. The LHAASO measurements imply that either additional emission sources exist or cosmic ray intensities have spatial variations.Comment: 12 pages, 8 figures, 5 tables; accepted for publication in Physical Review Letters; source mask file provided as ancillary fil

Structure-oriented prediction in complex networks

Complex systems are extremely hard to predict due to its highly nonlinear interactions and rich emergent properties. Thanks to the rapid development of network science, our understanding of the structure of real complex systems and the dynamics on them has been remarkably deepened, which meanwhile largely stimulates the growth of effective prediction approaches on these systems. In this article, we aim to review different network-related prediction problems, summarize and classify relevant prediction methods, analyze their advantages and disadvantages, and point out the forefront as well as critical challenges of the field

A One-dimensional Ubiquitiformal Constitutive Model for a Bi-material Rod

A one-dimensional linear elastic ubiquitiformal constitutive model for a bi-material rod under uniaxial tension is developed, in which, the explicit analytical expressions for both the effective elastic modulus and the displacement distribution are obtained. The calculated results of the effective elastic modulus for concrete are found to be in good agreement with previous experimental data

Research on one-dimensional ubiquitiformal constitutive relations for a bimaterial bar

A one-dimensional ubiquitiformal constitutive model for a bimaterial bar is proposed in this paper. An explicit analytical expression for the effective Young modulus is then obtained, which, unlike the fractal one, leads to a continuous displacement distribution along the bar. Moreover, numerical results for concretes are calculated and found to be in agreement with previous experimental data. In addition, some previous empirical and semi-empirical constitutive models are also examined, which shows that each of these models can correspond well to a ubiquitiformal one under a certain complexity

A stereological ubiquitiformal softening model for concrete

A stereological ubiquitiformal softening model for describing the softening behavior of concrete under quasi-static uniaxial tensile loadings is presented in this paper. In the model, both the damage evaluation process of fracture cross-sections and their distribution along the specimens axis are taken into account. The numerical results of a certain kind of full grade concrete made of crushed coarse aggregate are found to be in good agreement with the experimental data. Moreover, an experiental relation between the lower bound to the scale invariance of concrete and its tensile strength is also obtained by data fitting of the experimental data, which provides an effective approach to determine the lower bound to scale invariance of concrete

Diagnostic Value of Prospective Electrocardiogram-triggered Dual-source Computed Tomography Angiography for Infants and Children with Interrupted Aortic Arch

Background: Accurate assessment of intra- as well as extra-cardiac malformations and radiation dosage concerns are especially crucial to infants and children with interrupted aortic arch (IAA). The purpose of this study is to investigate the value of prospective electrocardiogram (ECG)-triggered dual-source computed tomography (DSCT) angiography with low-dosage techniques in the diagnosis of IAA. Methods: Thirteen patients with suspected IAA underwent prospective ECG-triggered DSCT scan and transthoracic echocardiography (TTE). Surgery was performed on all the patients. A five-point scale was used to assess image quality. The diagnostic accuracy of DSCT angiography and TTE was compared with the surgical findings as the reference standard. A nonparametric Chi-square test was used for comparative analysis. P <0.05 was considered as a significant difference. The mean effective radiation dose (ED) was calculated. Results: Diagnostic DSCT images were obtained for all the patients. Thirteen IAA cases with 60 separate cardiovascular anomalies were confirmed by surgical findings. The diagnostic accuracy of TTE and DSCT for total cardiovascular malformations was 93.7% and 97.9% (P > 0.05), and that for extra-cardiac vascular malformations was 92.3% and 99.0% (P < 0.05), respectively. The mean score of image quality was 3.77 ± 0.83. The mean ED was 0.30 ± 0.04 mSv (range from 0.23 mSv to 0.39 mSv). Conclusions: In infants and children with IAA, prospective ECG-triggered DSCT with low radiation exposure and high diagnostic efficiency has higher accuracy compared to TTE in detection of extra-cardiac vascular anomalies

Diffusion tensor imaging of thalamus in relapsing⁃remitting multiple sclerosis patients

Objective To investigate the presence of damage to the normal⁃appearing thalamus in relapsing⁃remitting multiple sclerosis (RRMS) and the relationship of diffusion tensor imaging (DTI) with the degree of disability of patients with RRMS. Methods Conventional MRI and DTI were acquired in 24 patients with relapsing ⁃remitting MS and 24 age ⁃ and sex ⁃ matched healthy volunteers. DTI parameters including fractional anisotropy (FA) and mean diffusivity (MD) were measured in normal⁃appearing thalamus by application areas of interest method. Group differences in MD and FA were examined and correlations between DTI parameters and clinical score of patients or lesion volume were investigated. Results Patients with RRMS had lower thalamic MD [(85.34 ± 14.68) × 10⁃3 mm2/s] than volunteers [(98.42 ± 13.10) × 10⁃3 mm2/s, t = ⁃ 3.257, P = 0.002], and higher FA (0.40 ± 0.04) than volunteers (0.36 ± 0.05, t = 3.163, P = 0.003). In patients with RRMS, MD values correlated with the Paced Auditory Serial Addition Test (PASAT) scores (r = 0.711, P = 0.000). Conclusion DTI was sensitive to detect abnormalities in normal⁃appearing thalamus of patients with RRMS. The association between thalamic DTI indexes and functional impairment suggests DTI is a promising marker of the RRMS for future studies. DOI：10.3969/j.issn.1672⁃6731.2012.02.01