Experimental Study on Source Failure Mechanism and Acoustic Emission Characteristics of Red Sandstone Under Uniaxial Compression

In order to study the rock fracture mechanism and precursor characteristics, uniaxial compression experiments of red sandstone were carried out. Using acoustic emission technology and digital speckle correlation method as experimental observation means, the evolution characteristics of deformation field and acoustic emission index during rock deformation were studied. The results show that : (1) The deformation concentration of rock deformation localization zone is the main cause of nonlinear evolution of rock stress-strain curve. (2) The volume parameters of different types of cracks in rock acoustic emission change with the relative displacement rate and dislocation rate of deformation localization zone. (3) In terms of failure types, there are more high-frequency components of tensile fracture main frequency, more low-frequency components of shear fracture main frequency, and wider distribution of mixed fracture main frequency. In the time sequence, the spectrum distribution of acoustic emission signals is wide and the amplitude is small at the sudden change time. At the sudden change time, the spectrum distribution of acoustic emission signals becomes narrow, the amplitude increases, and the spectrum distribution of peak points is greatly narrowed. Therefore, it is considered that the spectrum distribution is greatly narrowed can be used as an early warning precursor.

Experimental Study on the Relationship between Compression Stability and Deformation Localization of Viscous/Brittle Rock-Like Materials

Rock-like materials often exhibit irregular failure deformation under long-term service conditions, and the deformation and failure of asphalt and concrete materials is a serious problem that leads to subgrade failure. In this study, two different viscous/brittle rock-like materials were prepared by the in situ loading and optical speckle synchronous monitoring test method, and the evolution characteristics of the deformation field were studied during compression. The formation process of the compression deformation localization of rock-like materials and their relationship with stability were analyzed. A quantitative description of the compression deformation stage and localization characteristics of the viscous/brittle rock-like materials is presented. The results can be summarized as follows. At the initial stage of compression, the deformation localization zone of viscous/brittle rock-like materials begins to expand from the middle area to the surrounding area. Preliminary results of the deformation localization of the linear elastic deformation stage were obtained. The failure cloud image is completely formed at the peak, which is consistent with the failure physical map. The deformation process of compression can be quantitatively described using the deformation localization characteristics of rock-like materials.

A thermodynamically nonlocal damage model using a surface-residual-based nonlocal stress

ABSTRACT In this research, a surface-residual-based nonlocal stress was introduced into nonlocal damage theory to describe the long-range actions among microstructures that were excluded in the definition of Cauchy stress. By using the surface-residual-based nonlocal stress tensor, a thermodynamically consistent nonlocal integral damage model was established to simulate the strain localization behavior for elastic-brittle damage problems. In this model, both the strain and the damage were taken as nonlocal variables in the free energy function, and the integral-type damage constitutive relationships and the evolution equation were derived via thermodynamic laws in order to ensure the self-consistency within the thermodynamic framework. Based on the nonlocal damage formulations using a real nonlocal stress concept, we simulated the strain localization phenomenon in an elastic bar subjected to uniaxial tension. The results showed clear localizing and softening features of strain in the damage zone, and the boundary effects arising from the nonlocal surface residual were illuminated. Furthermore, the strain localization behaviors for different internal characteristic lengths were simulated, through which we found that the characteristic length was comparable to the size of the strain localization zone.

Tenosynovial Giant Cell Tumor in the Hand: Experience with 173 Cases

Background: Tenosynovial giant cell tumor (TSGCT) is the second most common benign tumor of the hand. Even though it is a benign lesion there is still a high incidence of local recurrence (range, 7%–44%) according to data in published papers. In this study, the clinical and epidemiological features of 173 patients who underwent excision of localized TSGCT, the recurrence rates and possible reasons for recurrence were examined in the light of current literature. Methods: Medical records of 173 patients with TSGCT were reviewed. Data on demographic characteristics as well as clinical and intraoperative findings were collected. Patients were asked about the recurrence of the TSGCT and the QuickDASH scoring was applied at the final clinical evaluation after mean follow-up of 81 months. Results: Females were predominantly involved (73%). Patients aged mean 44 years at the time of surgery. There were 93 tumors in flexor zones and 80 tumors in extensor zones of the hand. Of the tumors with flexor zone localization, zone II was most predominantly involved with 46 tumors, and 18 of these were on the index finger. The extensor zones III and IV were mostly involved with 9 tumors each on the middle and ring fingers. A total of 12 recurrences (6.9 %) were determined over the mean follow-up period of 81 months. Conclusions: The characteristics of our patients identified were similar to the previous studies. Surgical excision provides good outcomes in the treatment of TSGCT especially when clear margins are obtained.

A Visible and Near-IR Tunnel Photosensor with a Nanoscale Metal Emitter: The Effect of Matching of Hot Electrons Localization Zones and a Strong Electrostatic Field

The results of the research and design of a novel vacuum photosensor with a planar molybdenum blade structure are presented. The advanced prototype implements the principle of an increasing penetrability of the Schottky barrier for the metal–vacuum interfaces under the action of an external strong electrostatic field. Theoretical and experimental substantiation of the photosensor performance in a wide range of wavelengths (from 430 to 680 nm and from 800 to 1064 nm) beyond the threshold of the classical photoelectric effect is given. The finite element method was applied to calculate distribution of the optical and electrostatic fields inside the photosensor structure. The sensor current-to-light response was studied using the periodic pulsed irradiation with the tunable wavelength. It was shown that the nanoscale localization zones of two types are formed near the surface of the blade tip: the zone of an increased concentration of hot electrons localized inside the molybdenum blade, and the zone with an increased strength of the external electrostatic field localized outside the blade. In general, the mutual positions of these zones may not coincide, whereas the position of the first-type localization zone significantly varies with the changes in the wavelength of the irradiating light. This causes features in the spectrum of the quantum yield of the photosensor such as expressed non-monotonic behavior and occurrence of sharp dips. The design of the photosensor that provides matching of the positions for both types of localization zones was proposed; the manufactured prototypes of the designed device were experimentally studied. In the designed photosensor, the ballistic transport of photoelectrons in the vacuum gap with a strong field provides a possibility for the creation of ultra-fast optoelectronic devices, such as modulators, detectors, and generators.

Dermatoscopy in the diagnosis of pigmented nevi

The high incidence of melanoma and unsatisfactory results of its treatment in some cases make the issue of timely diagnostics of pre-melanoma skin pathology, in particular the identification of pre-melanoma pigmented nevi, of great importance and can be used for choice an adequate tactics of treatment. The purpose of the study was to evaluate the informativeness of dermatoscopy in cases of patients with pigmented nevi of skin as a part of melanoma prevention. 168 patients with pigmented nevi were screened. All nevi were photographed with a digital camera SONY Cyber-Shot DSC-H3, first in normal mode with the capture of the localization zone of the tumor and its surrounding tissues, and then in macro mode (“Zoom 10”). To confirm the clinical diagnosis, additional characteristics of the pigment formation on the skin, the manual immersion dermatoscopy, was used using the contact non-polarized HEINE mini 3000 LED dermatoscope. Evaluation of images was carried out using the diagnostic algorithm ABCD and ABCD-E. Our findings suggest that the clinical diagnostic algorithm used by us for detecting signs of the activation of a pigmented nevi is highly informative — the sensitivity is 97.6 %. Performing immersion dermatoscopy allows to increase the informativeness of the clinical and instrumental examination at the preoperative stage up to 98.2 %, which is comparable with the data obtained at the stage of urgent cytological examination: the method sensitivityis 98.2 %.

Atypical form of Retinopathy of Prematurity

Atypical forms of Retinopathy of Prematurity; including aggressive posterior retinopathy of prematurity (APROP), that can be seen despite normal birth week and weight, exhibits atypical localization (Zone 3), rapid progression, independent progression without a stage, and cannot be controlled by treatment. APROP is a disease that requires careful examination and making critical decisions, which can progress rapidly if not treated and result in retinal detachment and blindness. APROP requires attention and experience in terms of recognition and treatment approach. So, anti-VEGF's are in the foreground in their treatment either alone or combined with argon laser photocoagulation.

Кинетика развития паттернов макролокализации пластического течения металлов

The features of the macroscopic inhomogeneity of plastic deformation in the form of autowaves with a pulsating amplitude are analyzed, and data on the localization of sources of acoustic emission at different stages of plastic flow in the stretching of fcc mono- and polycrystals are presented. The relationship between the local components of the plastic distortion tensor in the strain localization zone is traced. The role of acoustic phenomena accompanying the localization of plastic strain in the development of the process of plastic deformation is considered.

ON ESTIMATE OF SIZE OF LOCALIZATION ZONE OF CARRIER OF SOLUTION TO A SEMILINEAR ELLIPTIC EQUATION

In this paper an estimate of size of localization zone of carrier of solution to the Dirichlet problem for a semilinear elliptic equation with measurable coefficients when the constant which limits the boundary conditions grows is defined more exactly.

What Happens beyond Drucker’s Proposition in Heterogeneous Media

This paper briefly reviews our recent analytical and experimental results on 3 interrelated features beyond the peak load in heterogeneous media: continuous bifurcation, damage localization and catastrophic rupture (CR). Firstly, an Elastic Statistically-Brittle model (ESB) was introduced to formulate the basic features of a kind of heterogeneous media, like rocks and cements. The global mean field approximation (GMF) shows that the measure of heterogeneity, like the Weibull modulus m in the distribution of meso-strength plays a key role to distinguish CR from gradual failure. Then, with the ESB model and corresponding experimental results, continuous bifurcation and damage localization are discussed. In accord with these, regional mean field approximation (RMF) is adopted and it shows that any scale of damage localization can satisfy the conservation laws in continuum mechanics. This implies that catastrophic rupture could appear at any state beyond the peak load, depending on the unknown evolution of damage localization zone. Hence, catastrophic rupture seems to occur stochastically at macroscopic level. On the other hand, both experimental and analytic studies demonstrate that a robust power law singularity (-1/2) appears ahead of CR. Preliminary applications of these ideas are briefly described.