Image Statistics Preserving Encrypt-then-Compress Scheme Dedicated for JPEG Compression Standard

In this paper, the authors analyze in more details an image encryption scheme, proposed by the authors in their earlier work, which preserves input image statistics and can be used in connection with the JPEG compression standard. The image encryption process takes advantage of fast linear transforms parametrized with private keys and is carried out prior to the compression stage in a way that does not alter those statistical characteristics of the input image that are crucial from the point of view of the subsequent compression. This feature makes the encryption process transparent to the compression stage and enables the JPEG algorithm to maintain its full compression capabilities even though it operates on the encrypted image data. The main advantage of the considered approach is the fact that the JPEG algorithm can be used without any modifications as a part of the encrypt-then-compress image processing framework. The paper includes a detailed mathematical model of the examined scheme allowing for theoretical analysis of the impact of the image encryption step on the effectiveness of the compression process. The combinatorial and statistical analysis of the encryption process is also included and it allows to evaluate its cryptographic strength. In addition, the paper considers several practical use-case scenarios with different characteristics of the compression and encryption stages. The final part of the paper contains the additional results of the experimental studies regarding general effectiveness of the presented scheme. The results show that for a wide range of compression ratios the considered scheme performs comparably to the JPEG algorithm alone, that is, without the encryption stage, in terms of the quality measures of reconstructed images. Moreover, the results of statistical analysis as well as those obtained with generally approved quality measures of image cryptographic systems, prove high strength and efficiency of the scheme’s encryption stage.

Interstage Pressures of a Multistage Compressor with Intercooling

This paper considers the criterion of minimum compression work to derive an expression for the interstage pressure of a multistage compressor with intercooling that includes the gas properties, pressure drops in the intercoolers, different suction gas temperatures, and isentropic efficiencies in each compression stage. The analytical expression for the interstage pressures is applied to estimate the number of compression stages and to evaluate its applicability in order to estimate interstage pressures in the operation of multistage compressors, which can be especially useful when their measurements are not available.

Near-single-cycle pulses generated through post-compression on FAB1 laser at ATTOLAB-Orme facility

Generating high-energy few-cycle pulses is key in the study of light-matter interaction in the regime of high field physics. Attosecond science possess the necessary time resolution to study the underlying fundamental processes but requires repetitions rates on the order the kilohertz and stabilization of the Carrier-Envelope Phase. We present here a post-compression stage delivering 3.8fs pulses with 2.5mJ coupled to a Ti: Sa based 1 kHz TW-class laser which can deliver 17.8fs pulses with 350mrad shot to shot CEP noise. This is the first step towards high-energy few-cycle post-compression of the FAB laser at ATTOLAB-Orme.

Pengaruh Tekanan Dan Tahap Kompresi Dalam Pemurnian Biogas Menjadi Biometana Dengan Absorpsi CO2 Menggunakan Air Bertekanan

Palm oil mill effluent (POME) from condensate stew, hydrocyclone water, and sludge separator contains organic carbon with a COD more than 40 g/L and a nitrogen content of about 0.2 and 0.5 g/L as ammonia nitrogen and total nitrogen. At present, the POME is converted into biogas using anaerobic ponds. Biogas produced contains 60% methane (CH4) and 40% carbon dioxide (CO2) and can be purified into biomethane through CO2 absorption using water. This study evaluates the optimum pressure and feed compression stage in biogas upgrading into biomethane. The results show the rate of circulation of water needed to separate CO2 from biogas feed decreases with increasing absorber pressure due to increased solubility of CO2 in water. Water circulation pumps and biogas compressor works increase due to the increase in pressure difference needed. The optimum pressure of the biogas biogas purification unit is within the range of 7-10 bar. At the same absorber pressure, the 1 stage feed compression unit is cheaper than that of 2 stages. However, the overall process with 1 compression stage might not be more economical than the 2-stage if consider the higher methane loss.

Finite element analysis of plasticity behaviour of aluminium alloys in high-pressure torsion compressive loading stage

Purpose The purpose of this paper is to examine the plasticity behaviour of aluminium alloys in high-pressure torsion (HPT) compressive loading stage. It is a part of the strengthen lightweight material development through severe plastic deformation. Design/methodology/approach A finite element simulation of HPT compression stage by displacement control incremental loading was proposed by taking into account an unconstraint HPT configuration. The quasi-static condition was utilised, by embedding strain hardening plasticity constitutive model and considering frictional effects, to assess the plasticity behaviour of aluminium alloys, particularly AA2024 and AA6082. Findings The present investigation clearly indicates that the deviation of material flow as a result of sticking condition of µ⩾0.5, was found to be negligible. An inhomogeneous material flow along the sample radial and thickness direction was evident, producing a stress concentration at the edge of the loaded surface, indicating the anticipated region of failure. The effective plastic strain in the compression stage was also found to be significant. Based on the effective strain response, plasticity behaviour of the compressed sample was predicted. Originality/value This paper demonstrates the plasticity behaviour of the analysed aluminium alloys. Since the mechanical properties produced by the deformed material are closely related to the exerted plastic deformation, understanding the phenomenon associated with the plastic strain development is essential. The outcome of this research will assist in seizing the opportunities of improving both material properties and the HPT procedures.

Upper Bound on the Joint Entropy of Correlated Sources Encoded by Good Lattices

Lattices provide useful structure for distributed coding of correlated sources. A common lattice encoder construction is to first round an observed sequence to a `fine’ lattice with dither, then produce the result’s modulo to a `coarse’ lattice as the encoding. However, such encodings may be jointly-dependent. A class of upper bounds is established on the conditional entropy-rates of such encodings when sources are correlated and Gaussian and the lattices involved are a from an asymptotically-well-behaved sequence. These upper bounds guarantee existence of a joint–compression stage which can increase encoder efficiency. The bounds exploit the property that the amount of possible values for one encoding collapses when conditioned on other sufficiently informative encodings. The bounds are applied to the scenario of communicating through a many-help-one network in the presence of strong correlated Gaussian interferers, and such a joint–compression stage is seen to compensate for some of the inefficiency in certain simple encoder designs.