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Controlled release matrices have predictable drug release kinetics, provide drugs for an extended period of time, and reduce dosing frequency with improved patient compliance as compared with conventional tablet dosage forms. In the current research work, losartan potassium controlled release matrix tablets were fabricated and prepared with rate altering agents; that is, Ethocel grade 100 combined with Carbopol 934PNF. Various drug to polymer ratios were used. HPMC, CMC, and starch were incorporated in some of the matrices by replacing some amount of filler (5%). The direct compression method was adopted for the preparation of matrices. In phosphate buffer (pH 6.8), the dissolution study was conducted by adopting the USP method-I as the specified method. Drug release kinetics was determined and dissolution profiles were also compared with the reference standard. Prolonged release was observed for all matrices, but those with Ethocel 100FP Premium showed more extended release. The co-excipient (HPMC, CMC, and starch) exhibited enhancement in the drug release rates, while all controlled release matrices released the drug by anamolous non-Fickian diffusion mechanism. This combination of polymers (Ethocel grade 100 with Carbopol 934PNF) efficiently extended the drug release rates up to 24 h. It is suggested that these matrix tablets can be given in once a day dosage, which might improve patient compliance, and the polymeric blend of Ethocel grade 100 with Carbopol 934PNF might be used in the development of prolonged release matrices of other water-soluble drugs.

Due to the angular deviation between the tunnel axis and the in-situ principal stress direction, the stress conditions of deep surrounding rocks become more notably intricate, giving rise to significant engineering geological disasters. This study aims to investigate the effect of the angle between principal stress and tunnel axis on the failure characteristics of surrounding rocks. To achieve this, a novel granite cuboid specimen featuring an oblique cylindrical hole was designed. The cylindrical hole was set at five angle levels (0°, 5°, 15°, 30°, and 45°) and two scenarios, including the rotation plane of the cylindrical hole parallel or perpendicular to the direction of the maximum principal stress σ1, were considered. A comprehensive investigation on the strain field around the hole and the mechanical response of the specimens was conducted through a series of biaxial compression tests, integrating acoustic emission and digital image correlation (DIC) detection, alongside the numerical simulations using discrete element method (DEM). The results revealed that the acoustic emission characteristics exhibited marginal variation as the rotation angle increased under biaxial compression. The predominant failure mode was a tension-shear failure, primarily governed by tensile cracks. The biaxial strength of the specimens exhibited a decreasing trend with the increase of horizontal rotation angle α. Conversely, the biaxial strength initially decreased, then increased, and ultimately decreased again with an increase in the vertical rotation angle β. An X-shaped high-strain band emerged around the hole when σ1 exceeded 60% of peak stress. As the rotation angle increased, this high-strain band extended into the interior of the specimens, with only a small portion visible on their surfaces. Numerical results confirmed that the failure characteristics inside the specimens aligned with those observed in physical test results. The spatial variation of micro-cracks in different specimens was thoroughly analyzed to discern the influences of the hole rotation angle on the failure behaviors.HighlightsAn innovative granite cuboid specimen featuring an oblique cylindrical hole was introduced.The strike direction effect of the cylindrical hole on the mechanical properties of granite specimens under biaxial compression was investigated.The experimental and numerical modeling approaches were employed to study the failure mode and microcrack distribution in rock specimens with an oblique cylindrical hole.

To investigate the strength and failure characteristics of rock mass, 3D discrete element method (DEM) is used in this study to conduct numerous simulated true triaxial compression tests on jointed marble. Three series of tests are carried out to study the influence of the intermediate principal stress and the joint inclined angle on the macroscopic mechanical characteristics. The DEM simulation results reveal that the strength and failure mechanism have a strong dependency on the intermediate principal stress except for the specimen with the inclined angle of 60° and the joint parallel to the intermediate principal stress direction. In addition, the influence of the joint inclined angle on the strength and failure characteristics is significant except for the specimen with the joint parallel to the minimum principal stress direction. Tensile cracks are the dominant failure mechanism. Based on a 3D true triaxial failure criterion, the simulated strength data can be predicted using four empirical parameters.

Bedding planes or layers can have a serious effect on the mechanical behaviour of shale rock. Fractures occurring along bedding planes form a fracture network in shale hydraulic fracturing; thus, the tensile strength and fracture mode are important for hydraulic fracturing design. In this research, shale disk specimens are prepared and analysed under Brazilian test conditions. During the test, a 3D digital image correlation system (DIC) is employed to capture surface deformation, and an AE sensor and strain observation system are, respectively, used to record the AE event and central strain of the shale disk during the failure process. A new inherently anisotropic model is established with a banded-particle model and smooth joint model using the particle flow code (PFC2D). The laboratory test result shows that the Brazilian tensile strength (BTS) value decreased gradually along with bedding inclination, which corresponds to a trend of the decrease of the strength over the entire interval, but it is a rather systematic decrease, approximating a linear variation. By considering the specimen after failure, three types of fracture patterns are observed: arc fracture (AF) through outside the central part, central fracture along the loading direction (LA) and mixed fracture patterns of the two. The DIC and central strain observation systems confirm that the split fractures do not always propagate along the diametrical loading direction, which means that the traditional isotropic elastic theory no longer works for layered shale. The micro-level failure behaviour and mechanism are analysed by PFC simulation. The PFC simulation reveals that the rock matrix tensile fracture and shear fracture along bedding plane are the main fracture pattern of shale disk specimens under the Brazilian test. The bedding inclination and interlayer bonding force play a very important role in the anisotropic behaviour of the shale.

The self-supporting capacity of the surrounding rock mass is a critical factor in maintaining tunnel stability after excavation and is a key determinant of tunnel support structures safety. Despite being widely applied, the mechanism behind the self-supporting effect remains a challenging issue to clarify. In this paper, we have used the finite difference method (FDM) to investigate the formation mechanism and characteristics of the surrounding rock mass's self-supporting zones. By analyzing the redistribution of a stress and an energy using stress concentration factor, energy concentration factor, we propose a self-supporting mechanism of the surrounding rock mass under different horizontal to vertical stress ratios. The further analysis results were subsequently validated through non-contact strain acquisition experiments. Our findings suggest that in cases of unequal horizontal and vertical stress, a “primary load-bearing zone” is formed in the direction of the vertical maximum principal stress within the rock mass. The rock mass areas aligned parallel to the direction of the maximum principal stress transfer the maximum principal stress to the primary load-bearing zone, causing compression towards the “primary load-bearing zone” and resulting in the formation of a “passive load-bearing zone”. The primary load-bearing zone resembles the footings of an arch, while the passive load-bearing zone resembles the arch's intrados. When the horizontal and vertical stresses are equal, the formation of the self-supporting zone is caused by the radial deformation of the surrounding rock into the tunnel cavity, followed by the mutual compression of the surrounding rock in the circumferential direction. The surrounding rock mass quality and depth of burial influence the size of the self-supporting zone, with the surrounding rock mass quality having a greater impact than the depth of burial.HighlightsAn analysis has been conducted to examine the differences between stress and energy redistribution after a tunnel excavation.An investigation has revealed the mechanism behind the formation of two types of load-bearing arches, namely the \"arch base supporting wedge-shaped arch\" and the \"compression around to the middle\", under different conditions after tunnel excavation.The influence of horizontal to vertical stress ratio, overburden depth and rock mass level on the extent and bearing capacity of the self-supporting zone is analyzed.

Storage systems often rely on multiple copies of the same compressed data, enabling recovery in case of binary data errors, of course, at the expense of a higher storage cost. In this paper, we show that a wiser method of duplication entails great potential benefits for data types tolerating approximate representations, like images and videos. We propose a method to produce a set of distinct compressed representations for a given signal, such that any subset of them allows reconstruction of the signal at a quality depending only on the number of compressed representations utilized. Essentially, we implement the holographic representation idea, where all the representations are equally important in refining the reconstruction. Here, we propose to exploit the shift sensitivity of common compression processes and generate holographic representations via compression of various shifts of the signal. Two implementations for the idea, based on standard compression methods, are presented: the first is a simple, optimization-free design. The second approach originates in a challenging rate-distortion optimization, mitigated by the alternating direction method of multipliers (ADMM), leading to a process of repeatedly applying standard compression techniques. Evaluation of the approach, in conjunction with the JPEG2000 image compression standard, shows the effectiveness of the optimization in providing compressed holographic representations that, by means of an elementary reconstruction process, enable impressive gains of several dBs in PSNR over exact duplications.

Pulse compression technology can augment the likelihood of target discernment without degradation and without amplifying system hardware requisites. However, radar-communication integrated waveforms may cause mismatches in reception due to communication modulation, leading to increased loss in processing gain (LPG). This method aims to achieve communication transmission while suppressing near-range sidelobe interference (NRSI) with a minor sacrifice in LPG. An environment-based weighted mismatched filter (EWMF) design methodology is proposed to attenuate NRSI to the requisite level, with further control of LPG possible by adjusting communication modulation parameters. Moreover, the alternating direction method of multipliers is employed to jointly optimize the integrated waveform and filter design. The effectiveness of this method is demonstrated using the average sidelobe level over a specified region as the performance metric. Theoretical evaluation and experimental results confirm the applicability of waveforms using EWMF, effectively suppressing NRSI, and this method is suitable for all waveforms based on pulse compression processing. Notably, it offers cost-reduction advantages without requiring modifications to the radar transmitter or receiver.

The identification of the disturbance stress direction of rock mass is crucial for safe and efficient production in underground engineering. This paper proposes a novel disturbance stress direction identification method of rock mass using acoustic parameters, which can provide precise disaster protection in underground engineering. First, monitoring sensors are arranged in the target rock mass area for environmental preparation and data acquisition. Second, the acquired data are cleaned and the parameter weight is carefully balanced. Third, the objective function is constructed and the disturbance stress direction is identified. To verify the validity of the proposed method, the uniaxial and biaxial compression tests on granite specimens were carried out to simulate the engineering disturbances on the rock mass under equal and non-equal confining pressure conditions, respectively. The results showed that the average direction error of the novel method is 12.74°. The accuracy of the proposed method could be enhanced by dealing with rock mass in isobaric conditions and a larger dataset. This study not only achieves effective identification of disturbance stress direction but also contributes to preventing and controlling engineering disasters.HighlightsA novel disturbance stress direction identification method (DSDI) using acoustic parameters is proposed.The structural change of rock masse induced by disturbance stress is the inherent cause of anisotropy in acoustic parameter variations.The accuracy of DSDI was verified by the indoor experiment under equal confining pressure and non-equal confining pressure.

The direction-of-arrival (DoA) estimation algorithms have a fundamental role in target bearing estimation by sensor array systems. Recently, compressive sensing (CS)-based sparse reconstruction techniques have been investigated for DoA estimation due to their superior performance relative to the conventional DoA estimation methods, for a limited number of measurement snapshots. In many underwater deployment scenarios, the acoustic sensor arrays must perform DoA estimation in the presence of several practical problems such as unknown source number, faulty sensors, low values of the received signal-to-noise ratio (SNR), and access to a limited number of measurement snapshots. In the literature, CS-based DoA estimation has been investigated for the individual occurrence of some of these errors but the estimation under joint occurrence of these errors has not been studied. This work investigates the CS-based robust DoA estimation to account for the joint impact of faulty sensors and low SNR conditions experienced by a uniform linear array of underwater acoustic sensors. Most importantly, the proposed CS-based DoA estimation technique does not require a priori knowledge of the source order, which is replaced in the modified stopping criterion of the reconstruction algorithm by taking into account the faulty sensors and the received SNR. Using Monte Carlo techniques, the DoA estimation performance of the proposed method is comprehensively evaluated in relation to other techniques.

The evaluation of rock mechanic characteristics of shale reservoir is the key for the success of fracturing. Several limitations such as complex lithology can affect the accuracy of the rock mechanic property computation. In this research, the mechanical rock properties of shale reservoirs were analyzed based on experimental tests including shale-reservoir mineral composition, uniaxial compressive strength, and triaxial compression tests. The results showed that (1) the difference in mineral composition leads to easier fracturing of sand shale reservoirs compared with pure shale reservoir. (2) Under uniaxial conditions, the rock mechanical parameters along the vertical bedding direction of sand shale reservoirs are better than pure shale reservoir parameters. The mechanical properties of shale reservoirs in parallel bedding direction are less affected by lithology. Under triaxial conditions, the confining pressure increases more than 4.0 times with the compressive strength of rocks, and the rock Young’s modulus in the parallel bedding direction is higher compared with the vertical bedding direction. (3) Rock failure mode is mainly subdivided into cutting and splitting modes, and the bedding features of rock mechanic properties highly influence the drilling and fracturing operations. This study offers guidelines for the optimization of the drilling and fracturing process based on accurate evaluation of the rock mechanical properties.