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The frequent occurrence of casing failure has significantly affected the development of shale gas in the Sichuan Basin. Based on engineering and geology analyses, natural fracture/fault slip leads to casing shear deformation during hydraulic fracturing. Hence, natural fracture/fault slip and casing‐cement sheath‐formation assembly finite element models were established to quantitatively examine the characteristics of natural fracture/fault slip and mechanisms of casing shear deformation. Many factors, such as formation elastic property, in situ stress, natural fracture/fault geometry property, fluid pressure, casing elastic property, cement sheath elastic property, and well trajectory, were considered. The simulated results were in good agreement with the field data. The results indicated that natural fracture/fault slip leads to a sharp increase in casing deformation and stress in the adjacent region. Furthermore, factor sensitivity analysis results showed that a higher fluid pressure, larger fracture length, larger fracture dip angle, higher in situ stress difference, lower formation Young's modulus, and shorter distance from the wellbore to the center of the slip surface lead to severe casing stress and deformation. The countermeasures for preventing casing shear deformation involve decreasing the fracturing treatment pressure, reducing the crossing angle between the wellbore and natural fracture/fault, maintaining a safe distance from the wellbore to the large fracture/fault center, and adopting “balanced stress” fracturing operation. Hence, this study proposes a reasonable method to evaluate casing shear damage under hydraulic fracturing.

In this study, new kinds of hydrogen-bonded (H-bonded) chiral molecular switches (CMS) composed of azobenzene moieties as photo-responsive parts and H-bonded complexes as thermo-responsive parts were developed. Photo- and thermally-reversible switching behavior of cholesteric liquid crystals (Ch-LCs) based on the H-bonded CMS was investigated in detail. The results demonstrate that H-bonded CMS undergo a trans–cis photoisomerization under UV light, which results in the decrease of helical twisting power (HTP). Meanwhile, the modulation of the intermolecular forces between proton donors and acceptors with temperature has a positive influence on the change in HTP. Reversible blue, green, and red reflections of the self-organized helical superstructure could be achieved under UV/Vis light as well as with temperature change. According to the geometry optimization based on Gaussian 03 calculations at the B3LYP/6-31G(d) level, the molecular aspect ratio could be considered to be one of the important factors influencing the HTP of H-bonded CMS. This dynamic tuning of the self-organized helical superstructure based on dual and selective molecular mechanism opens up a way to achieve new kinds of LC photonic materials.

A novel class of hydrogen-bonded chiral azobenzene switches was developed to induce an optically tunable liquid crystal blue phases (LC-BPs), which leads to the stabilization of the LC-BPs for a wider temperature range and is capable of a reversible phototuning of the reflection color of BP I over the visible wavelength region.

A novel series of photoresponsive chiral switches are fabricated by a facile hydrogen-bonded (H-bonded) assembly method, in which the binaphthyl azobenzene molecule is used as the proton acceptor, and binaphthyl acids with opposite chiral configuration are proton donors. We find that the helical twisted power of H-bonded chiral switches and the helical handedness of induced chiral nematic liquid crystals (N*-LCs) are mainly determined by the terminal flexible chain length in proton donors of binaphthyl acids. Controlling the lengths of the terminal flexible chain leads to different photoswitching behaviors by light irradiation, such as a helical inversion in the N*-LCs and a phase transition from N*-LCs to nematic LCs. This is mainly because of chiral counteraction and intensity attenuation of opposite chiral configurations between the proton acceptor and proton donor during UV-vis irradiation. Additionally, the thermal switching behavior of N*-LCs doped with H-bonded chiral switches is also demonstrated, and the related tuning mechanism may be attributed to the H-bonded effect and the changes in a dihedral angle of the binaphthyl rings. This facile assembly approach provides a new way for the fabrication of functional chiral switches for photonic applications.

An efficient angle-rotation architecture, suitable for use in a digital mixer, is presented. The architecture employs a decomposition of the high-precision rotation-angle into a coarse angle and a fine angle, and employs two processing stages, coarse and fine. Only the coarse stage employs a ROM, and that ROM is extremely small. Small multipliers are shown to suffice while providing full accuracy at the system output. A systematic development of the architecture and its supporting theory and assumptions is given, along with the rationale for determining its structure. A rigorous analysis of its error sources is presented, as well as the computation of bounds for the various errors they induce at the system output. This error analysis is shown to lead to a straightforward means of designing an efficient two-stage angle-rotation unit for a digital mixer, given input/output bitwidths and performance specifications

In an all-digital timing-adjustment system for digital modems, interpolation can be employed to recover samples that are synchronous with the data symbols. In this paper, a novel interpolation method is described for such systems. Instead of approximating a continuous-time signal with a conventional (algebraic) polynomial and computing the synchronized samples using a Farrow structure, a trigonometric polynomial is employed. It is demonstrated that this approach produces a particularly simple implementation structure, reduces computational delay and, for practical signals, can improve the interpolation performance. Moreover, to recover a synchronized sample from existing samples, given a timing offset, it is shown that the method can be optimized such that a recovered sample's interpolation error is minimized for that specific timing offset value. The input signal's spectrum is also taken into account. Simulation results indicate that the method can achieve the best performance among all state-of-the-art methods tested. In addition, the optimal interpolator can be implemented without increased hardware requirements.

This paper describes the architecture and IC implementation of a rectangular-to-polar coordinate converter for digital communication applications. The architecture core uses small lookup ROMs, fast multipliers, and a single angle-rotation stage. Area and latency are reduced in comparison with traditional methods. The processor, implemented in 0.25-/spl mu/m five-metal CMOS, has 14-b in-phase and quadrature channel inputs and 15-b magnitude and phase channel outputs. The phase and magnitude calculations have a maximum error of 0.00024 (0.0078% of /spl pi/) and 0.03 (1% of 2/spl radic/2), respectively. Computational latency is 19 cycles, and power dissipation is 470 mW at 2.5 V and 406 MHz (Mconversions/s).

A 300-MHz quadrature direct digital frequency synthesizer/complex mixer (QDDSM) chip is presented. With a 32-bit input frequency control word, the tuning resolution is 0.07 Hz at the operating frequency of 300 MHz. The 12-bit I and Q inputs and 13-bit I and Q outputs offer a spurious-free dynamic range of 90.3 dB. The tuning latency is 13 clock cycles, which corresponds to 43 ns at 300 MHz. The tuning bandwidth (half the operating frequency) is 150 MHz. The IC is realized in 0.25-/spl mu/m TSMC CMOS technology with 4180 standard library cells and occupies a core area of 0.36 mm/sup 2/. At 300 MHz, the power dissipation is less than 400 mW. A key feature of the design is the creation of conditionally negating multipliers.

A reconfigurable angle rotator architecture is proposed and incorporated into an energy-efficient reconfigurable FFT/IFFT processor IC as its major computation component, endowing the FFT/IFFT processor with a significant scalable power dissipation feature with varying FFT size. The reconfigurability of the angle rotator is realized by dynamically allocating computation resources, which are subrotation stages in cascade. This approach tends to minimize the size of the lookup table while maintaining computation accuracy, and tends to minimize the area and power consumption while improving the overall performance.

With a 32-bit frequency-control-word and two 15-bit (I and Q) data inputs, while employing less hardware than a conventional 2-multiplier/DDFS approach, this interleaved IC provides a quadrature DDFS (nearly for free!) with 100 dB spurious-free dynamic range and produces a 16-bit modulated sinusoidal output. Power dissipation is 0.5 W at an 830 MHz clock-rate with a 2.5 V supply.

A 400-MHz digital rectangular-to-polar coordinate converter has been implemented in 0.25-/spl mu/m CMOS. The inputs to the chip are 14-bit in-phase and quadrature channels, and the outputs are 15-bit magnitude and phase channels. The phase and magnitude calculations have a maximum error of 0.00024 and 0.03, respectively. At a maximum frequency of 406 MHz, the circuit dissipates 470 mW of power at 2.5 V.

In many communication system implementations, such as M-ary PSK and FSK modems, DMT for ADSL, as well as carrier and clock synchronization, the efficient conversion from rectangular to polar coordinates is essential. In this paper, we present a novel architecture for a circuit that computes the angle, as well as the magnitude, of a polar-form representation of a complex number, given the real and imaginary components of that number.

The use of interpolation for the adjustment of timing offset in digital modems has attracted increasing attention. We recently announced a novel interpolation method which, instead of approximating the continuous-time signal with a conventional polynomial and computing the synchronized samples using a Farrow structure, uses a trigonometric polynomial. Simulation results indicate that improved performance, reduced computational delay and, in most cases, simplified hardware can be achieved. In this paper, we formulate our method in terms of a digital interpolation filter. We then show that with a slight modification of our original method, the interpolation filter based on the trigonometric polynomial can achieve a desired frequency response.

We present an architecture for high performance sine/cosine generation and angle rotation. Unlike CORDIC-type methods, which implement rotation using a sequence of subrotation stages, each realized, with a butterfly structure, the proposed approach implements the rotation with just two stages. We perform approximately the same number of arithmetic operations in our architecture as in CORDIC-type processors, but our architecture consolidates the operations into small array-multipliers, which can yield a smaller and faster circuit using well-known efficient multiplier implementation techniques (such as Booth encoding).

All-digital approaches for the adjustment of timing offset in digital modems have attracted increasing attention. We recently announced a novel interpolation method which, instead of approximating the continuous-time signal with a conventional polynomial and computing the synchronized samples using a Farrow structure, uses a trigonometric polynomial. Simulation results indicate that improved performance, reduced computational delay and, in most cases, simplified hardware can be achieved. To recover a synchronized sample from existing samples, given a timing offset, we show here that we can optimize this method such that the interpolation error in the recovered sample is minimized for that specific timing offset value. Using this optimization technique, the overall interpolation error is reduced. As for the implementation, the optimal interpolator does not require additional hardware as compared to our original method.

In burst-mode data transmission used in GSM and IS-136, rapid acquisition of the symbol timing and the carrier phase from the observation of a short signal-segment is essential. Feedforward timing recovery is well suited for such transmissions due to its rapid acquisition characteristics. For personal mobile communications where low complexity and low power are the major requirements, it is desirable to sample the signal at the lowest possible rate and to have the synchronizer be as simple as possible. In this paper we propose a synchronizer for initial timing and carrier-phase estimation using preambles. The synchronizer needs just two samples per symbol period and it exhibits good performance, even for signals employing small excess bandwidth. These estimations can be obtained directly from the burst detector output. We also show that the synchronizer can be implemented very efficiently.

We present the fixed-point analysis and realization of a blind beamforming algorithm. This maximum-power beamforming algorithm consists of the computation of a correlation matrix and its dominant eigenvector, and we propose that the later be accomplished by the power method. After analyzing the numerical stability of the power method, we derive a division-free form of the algorithm. Based on a block-Toeplitz assumption, we design an FIR filter based system to realize both the correlation computation and the power method. Our ring processor, which is optimized to implement digital filters, is used as the core of the architecture. A special technique for dynamically switching filter inputs is shown to double the system throughput. Finally we discuss the issue of hardware/software hybrid realization.

In this study, we develop a kind of novel photoswitchable chiral azo switches bearing both axially chiral binaphthyl center and single tetrahedrally chiral center with different configurations. The influence of the configuration of the tetrahedrally chiral centers and the introduction of a rigid structure on the helical twisting power (HTP) of the chiral azo switch was addressed in detail. Our results demonstrate that the import of the tetrahedrally chiral center dramatically decreased the HTP of the axially chiral azo switch, while the rigid long core increased the HTP. According to a molecular simulation based on Gaussian03 calculations at the B3LYP/6-31G(d) level, both the molecular configuration and the molecular aspect ratio were found to be the key factors influencing the HTP of the chiral azo switch. Finally, we utilize the above chiral azo switch to fabricate a photo-addressed, flexible liquid crystal device. This work provides an insight into the relationship between the chiral effect and molecular structure of chiral switches and their potential applications for photonic and display fields.