Channeling Technique Research Articles

Lattice location and annealing studies of Hf implanted CaF2

Hafnium ions were implanted into calcium fluoride single crystals. The lattice damage introduced by the implantation was investigated with the Rutherford backscattering (RBS) channelling technique. The lattice location of the implanted ions was determined by performing channelling measurements for the 〈110〉 crystal direction. A comparison of the angular scan with Monte Carlo simulations leads to the conclusion that >90% of the Hf ions are on Ca sites directly after implantation. Subsequent annealing of the samples was performed in a rapid thermal annealing apparatus. Perturbed angular correlation (PAC) measurements with 181Hf(181Ta) show quadrupole interactions with νQ1=300(3) MHz (η=0.00), νQ2=1285(13) MHz (η=0.43) and νQ3=1035(10) MHz (η=0.00) after annealing up to 1200K.

Ecological restoration design of a stream on a college campus in central Ohio

Straightened stream channels and altered and drained wetlands have adversely impacted streams and rivers throughout Midwestern USA, where some of the most dense drainage and riparian ecosystem alteration in the world have occurred. A segment of Grave Creek on The Ohio State University's Marion (OSU Marion) campus in Ohio, USA, with its lack of riparian ecosystems, illustrates the transformation of a natural fluvial ecosystem to an unstable and “simplified” aquatic environment that requires continued maintenance and provides little value to the surrounding landscape or to the university. However, the straight ditch, available adjacent riparian land and existing hydric soil give OSU Marion a great opportunity to demonstrate a project of stream and wetland restoration on a college campus. To restore the natural ecological stability of OSU Marion's “back yard” and to provide habitat improvement to Grave Creek and its surrounding landscape on the OSU Marion campus, we have designed a restoration of 1.1 km of Grave Creek meandering to the east of the existing sewer, using the two-stage channel techniques, and about 0.6–0.8 ha of adjacent wetland. We estimate that restoration on this scale will cost about US$ 200,000–300,000, not including monitoring of the results. To fulfill this project, it is likely that an opportunity for using this restoration in a stream/wetland loss mitigation will present itself in this region of Ohio while a long-term pre- and post-construction monitoring plan and more detailed design would be expected as the next step.

Effect of fluence on the lattice site of implanted Er and implantation induced strain in GaN

A GaN thin film was implanted with 5×1014cm−2 of 60keV stable 166Er, followed by the implantation of 2×1013cm−2 radioactive 167Tm (t1/2=9.3d) and an annealing sequence up to 900°C. The emission channeling (EC) technique was applied to assess the lattice location of Er following the Tm decay from the conversion electrons emitted by 167mEr, which showed that more than 50% of 167mEr occupies substitutional Ga sites. The results are briefly compared to a 167mEr lattice location experiment in a GaN sample not pre-implanted with 166Er. In addition, high-resolution X-ray diffraction (HRXRD) was used to characterize the perpendicular strain in the high-fluence implanted film. The HRXRD experiments showed that the Er implantation resulted in an increase of the c-axis lattice constant of the GaN film around 0.5–0.7%. The presence of significant disorder within the implanted region was corroborated by the fact that the EC patterns for off-normal directions exhibit a pronounced angular broadening of the order of magnitude of 0.5°.

An overlapping and pipelining data transmission MAC protocol with multiple channels in ad hoc networks

In mobile ad hoc networks (MANETs), the IEEE 802.11 DCF protocol is commonly used at the medium access control (MAC) layer to reduce collision and contention. However, mobile nodes, before send out data, need to wait for other in-process data transmission in the same range to be completed. In this paper, we address this performance degradation problem in the DCF mechanism and propose an overlapping and pipelining data transmission MAC protocol to enhance throughput. The protocol regulates the actions of the neighboring nodes of both the sender and the receiver and enables the utilization of the same channel simultaneously by these neighboring nodes. A multiple sub-channel technique is proposed to avoid the interference problem caused by the control and data signals of different communication mobile node pairs. With the regulated actions and the multiple channel technique, multiple pairs of mobile nodes are provided with the desired feature of utilizing the same data sub-channel simultaneously without interfering with one another. Although the overlapping data transmission technique can increase the number of simultaneous communication pairs, an efficient bandwidth allocation of the control and data sub-channels to maximize utilization is critically important. Therefore, we further propose a bandwidth allocation strategy in which the control signals and data signals are pipelined. Performance simulation results prove the efficiency of the proposed bandwidth allocation strategy with better channel utilization. In addition, the proposed MAC protocol with the bandwidth allocation strategy, combined with the overlapping and pipelining data sub-channel technique, outperforms the IEEE 802.11 DCF in throughput (kB/s) by about 43.76%.

Comparison and analysis of equalization techniques for the time-varying underwater acoustic channel.

It has long been accepted that adapting a decision feedback equalizer in a time‐varying environment by first estimating the channel impulse response and using this estimate to calculate equalizer tap coefficients results in better performance than is achieved by directly adjusting the equalizer taps. There are several empirical demonstrations in the literature, [Shukla and Turner, IEE Proc.‐Commun. 138, 525–543 (1991)], but the explanations for the performance difference are varied and none uses analytical arguments. Analysis shows that at high signal‐to‐noise ratio (SNR) for time varying channels, the taps of the feed‐forward equalizer fluctuate more rapidly than do the taps of the channel impulse response and using channel estimate based adaptation is more effective. The largest changes in the equalizer coefficients occur when the input signal correlation matrix has a large condition number. At low SNR the matrix is better conditioned and the performance gap disappears. These results assume that the del...

A 2D numerical simulation of sub-cooled flow boiling at low-pressure and low-flow rates

The main purpose of this study is to apply a two-fluid mathematical model to numerical simulation of two-phase flow at low-pressure condition. Although models of sub-cooled boiling flow at one-dimension and high-pressure have been studied extensively, there are few equivalent studies for numerical simulation at two-dimension and low-pressure (1–2 bar) conditions. Recent literature studies on sub-cooled boiling flow at low-pressure have shown that empirical models developed for high-pressure situations are not valid at low-pressures. Since the mathematical model used in this study is accomplished at low-pressure, the transport equations for the variables of each phase are substituted in low-pressure. The governing equations of two-phase flow with an allowance to inter-phase transfer of mass, momentum and heat, are solved using a two-fluid; non-equilibrium model. The finite volume discretization scheme is used to create a linearized system of equations that are solved by SIMPLE staggered grid solution technique for a rectangular channel. Improvement of the void fraction prediction of our model for the case of low-pressure sub-cooled flow boiling conditions was achieved. It is found that the heat transfer due to evaporation and surface quenching is higher than that by convection. Good agreement is achieved with the predicted results against the experimental data’s available in the literatures for a number of test cases.

Strain enhancement in Si induced by direct bonding of a LaAlO 3 film to a Si substrate

The depth profiles of lattice strain near the interface regions of LaAlO 3/Si and the SiO 2 interfacial layer/Si were investigated by the ion channeling technique using high-resolution Rutherford backscattering spectroscopy (HRBS). In the case of the LaAlO 3/Si stack, horizontal tensile strain in the Si near the interface was clearly observed. However, this strain was relaxed by formation of the interfacial layer through annealing in an oxygen ambient. These results suggest that the strain in Si induced by a dielectric strongly depends on the material in contact with Si.

Performance Improvement of Wireless Mesh Networks by Using a Combination of Channel-Bonding and Multi-Channel Techniques

In the present paper, the use of a combination of channel-bonding and multi-channel techniques is proposed to improve the performance of wireless mesh networks (WMNs). It is necessary to increase the network throughput by broadening the bandwidth, and two approaches to effectively utilize the broadened bandwidth can be considered. One is the multi-channel technique, in which multiple separate frequency channels are used simultaneously for information transmission. The other is the channel-bonding technique used in IEEE 802.11n, which joins multiple frequency channels into a single broader channel. The former can reduce the channel traffic to mitigate the effect of packet collision, while the latter can increase the transmission rate. In the present paper, these two approaches are compared and their respective advantages are clarified in terms of the network throughput and delay performance assuming the same total bandwidth and a CSMA protocol. Our numerical and simulation results indicate that under low-traffic conditions, the channel-bonding technique can achieve low delay, while under traffic congestion conditions, the network performance can be improved by using multi-channel technique. Based on this result, the use of a combination of these two techniques is proposed for a WMN, and show that it is better to use a proper channel technique according to the network traffic condition. The findings of the present study also contribute to improving the performance of a multimedia network, which consists of different traffic types of applications.

The Malone Antegrade Continence Enema: Single Institutional Review

We report the long-term outcome of the Malone antegrade continence enema procedure in the treatment of chronic constipation and fecal incontinence in children with neuropathic bowel. We performed a retrospective chart review of 256 Malone antegrade continence enema procedures. Patient age at surgery, bowel segment used, location of stoma, number and type of revisions required, and fecal continence were documented and a database was created. A total of 236 patients with at least 6 months of followup are included in this report. There were 172 in situ appendicocecostomies, 23 split appendix channels, 9 appendicocecostomies with cecal extension, 22 Yang-Monti ileocecostomies and 10 colon flap channels performed. A total of 112 males (47%) and 124 females (53%) were included in the study. Median patient age at surgery was 9 years (range 2 to 36) and median followup for the entire cohort was 50 months (6 to 115). A total of 56 surgical revisions were performed in 39 patients (17%). Median time to first revision was 9.5 months (range 1 to 105). Stomal stenosis occurred in 32 patients (14%). Overall, surgical revisions were required in 14% of in situ appendix channels (24 of 172), 22% of split appendix channels (5 of 23), 33% of appendix channels with cecal extension (3 of 9), 18% of Yang-Monti Malone antegrade continence enema channels (4 of 22) and 30% of colon flap channels (3 of 10). Independent of channel technique, surgical revisions were required in 15% of umbilical stomas and 18% of lower quadrant stomas (p = 0.516). Two patients had minimal stomal leakage, and 94% (221 of 236) achieved fecal continence with irrigations. The long-term results of the Malone antegrade continence enema channel in a large cohort of patients with neuropathic bowel and chronic constipation are encouraging. Of the patients 17% will require revision surgery, and patients/parents should be counseled accordingly. In our series in situ appendicocecostomy had the lowest revision rate on long-term followup, although the difference was not statistically significant (p = 0.226).

A GA-Based Effective Fault-Tolerant Model for Channel Allocation in Mobile Computing

Efficient channel allocation to mobile hosts is of utmost importance in a cellular network. A genetic algorithm (GA), which is a useful tool in solving optimization problems, is explored to design a fault-tolerant cellular channel allocation model that allows a cell to continue communicating with its mobile hosts, even if there are insufficient channels available in the cell. Sometimes, the load over a cell may increase to the extent that it needs more channels than it actually has in order to handle the traffic. On the other hand, it is quite possible that the load in some other cell is less than its channel capacity, resulting in underutilization of the channels. This problem is solved by temporarily taking unutilized channels from cells that have lesser load and allocating them to the cells that are overloaded. We propose a model that reuses available channels more efficiently. The model also considers the handoff by using the reserved channel technique. A reserved pool of channels makes the model fault tolerant. Thus, the proposed work uses GA for fault-tolerant dynamic channel allocation to minimize the average number of blocked hosts and handoff failures in the mobile computing network. Simulation experiments evaluate the performance of the proposed model. Comparison of the results with the two recent earlier models reveals that the proposed model works better in serving mobile hosts.

Electrodeposition of cobalt based ferro-magnetic metal nanowires in polycarbonate films with cylindrical nanochannels fabricated by heavy-ion-track etching

Polycarbonate films of thickness 30 μm were irradiated with heavy ions by applying a flux of 108 ions cm−2 to produce straight tracks perpendicular to the film surface. The tracks were preferentially etched in 6 M aqueous solution of sodium hydroxide to prepare cylindrical nanochannels. The channel diameters were tuned between 200 and 600 nm by varying the etching time. Co81Cu19 alloy nanowires were electrodeposited potentiostatically, while Co/Cu multilayered nanowires, consisting of alternating Co and Cu layers with thickness 10 nm, were synthesized by means of a pulse plating technique in channels of length 30 μm and diameter 200 nm. Co81Cu19 alloy nanowires showed an anisotropic magnetoresistance effect of 0.6%, and the giant magnetoresistance of Co/Cu multilayered nanowires reached up to 8.0%.

Stable Transmission in the Time-Varying MIMO Broadcast Channel

Both linear and nonlinear transmit precoding strategies based on accurate channel state information (CSI) can significantly increase available throughput in a multiuser wireless system. With propagation delay, infrequent channel updates, lag due to network layer overhead, and time-varying node position or environment characteristics, channel knowledge becomes outdated and CSI-based transmission schemes can experience severe performance degradation. This paper studies the performance of precoding techniques for the multiuser broadcast channel with outdated CSI at the transmitter. Traditional channel models as well as channel realizations measured by a wideband channel sounder are used in the analysis. With measured data from an outdoor urban environment, it is further shown the existence of stable subspaces upon which transmission is possible without any instantaneous CSI at the transmitter. Such transmissions allow for consistent performance curves at the cost of initial suboptimality compared to CSI-based schemes.

Activation of the CFTR Cl- Channel by Trimethoxyflavone in vitro and in vivo

The flavone apigenin has been previously selected as a potent pharmacological activator of the CFTR Cl^- channel, however, its utility for the activation of CFTR in vivo is expected to be limited because flavonoids are readily metabolized. We therefore investigated the poorly metabolizable methylether of apigenin, 5,7,4’-trimethoxyflavone (TMF) as a CFTR activator using transepithelial short-circuit current measurements, whole cell and single cell patch clamp techniques, and nasal potential difference (PD) measurements. Transepithelial Cl^- secretion by Calu-3 epithelia was stimulated by TMF with a halfmaximal concentration of 64±5 μM to 55±15% of maximal currents achieved by subsequent addition of cAMP agonist forskolin (10 μM). In forskolin-prestimulated tissues, TMF showed small effects and stimulated Cl^- secretion by an additional 6%. Single channel and whole cell patch clamp techniques were used to verify these effects and identify CFTR as the target of TMF. TMF increased the open probability of silent CFTR (to 0.31±0.06) but showed small effects once CFTR had been prestimulated with forskolin. In nasal PD measurements in humans, perfusion of TMF onto the nasal mucosa activated nasal PD by -9.5±1.1 mV, which was 69% of the effect of TMF+isoproterenol (-13.8±3.9 mV). These data show that TMF is an activator of CFTR in both in vitro and in vivo assays that targets mainly the unstimulated CFTR.

Identification of noise modes for automobile operational modal analysis

In rotating machinery, the input excitation does not meet the requirement of operational modal analysis (OMA). In this article, an effective and improved method of distinguishing forced harmonic response from measured vibration signal is presented based on the differences of the statistical properties of a stochastic signal and a harmonic signal. It makes the OMA applicable to the situation of existing periodic excitation. In order to prove the effectiveness of the proposed method, a modal experiment of a steel plate excited by a motor is performed. Then, an OMA is performed to solve the vehicle interior noise problem. Combining the projection channel technique with the advanced method, most noise modes, especially harmonic modes are successfully separated. Precise modal parameters of the car are obtained in typical working conditions which provide guidance of the dynamic modification and show that the harmonic identification method has great practical value.

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HRBS/channeling studies of ultra-thin ITO films on Si

High-resolution Rutherford backscattering spectroscopy (HRBS)/channeling techniques have been utilized for a detailed characterization of ultra-thin indium tin oxide (ITO) films and to probe the nature of the interface between the ITO film and the Si(001) substrate. Channeling studies provide a direct measure of the lattice strain distribution in the crystalline Si substrate in the case of amorphous over layers. The measurements on DC magnetron sputtered ITO films have been carried out using the recently installed HRBS facility at the Centre for Ion Beam Applications (CIBA). The thickness of the ultra-thin (∼9.8nm) ITO films was calculated from the HRBS spectra having an energy resolution of about 1.4keV at the superimposed leading (In+Sn) edge of the ITO film. The films were near stoichiometric and the interface between ITO film and Si was found to include a thin SiOx transition layer. The backscattering yields from (In+Sn) of ITO were equal in random and channeling directions, thereby revealing the non-crystalline nature of the film. Angular scans of HRBS spectra around the off-normal [111] axis clearly showed a shift in the channeling minimum indicative of compressive strain of the Si lattice at the SiOx/Si interface. The observed strain was about 0.8% near the interface and decreased to values below our detection limits at a depth of ∼3nm from the SiOx/Si interface.

Leak location using blind system identification in water distribution pipelines

This paper presents a new leak location method without knowledge of pipe length in water distribution pipes. In conventional leak location surveys using acoustic signals in buried water distribution pipelines, the most widely used techniques are based on the correlation technique. The prerequisite of the method is that the accurate length of pipeline between two detection points is known. However, in practice, this prerequisite is not always satisfied. Based on the fact that the acquired acoustic signals contain the characteristics related to the two propagation channels, the blind system identification strategy is applied to estimate the transmission performances of the two acoustic channels. Due to the long impulse response of acoustic channel, the overlap-save and cross-correlation fitting technique are utilized in blind system identification to estimate the acoustic channels under a built constraint condition. In order to avoid converging to the local minima, the genetic algorithm is adopted to optimize the channel identification. The times due to the propagation of the leak source signal traveling from the leak point to either sensor are extracted from the identified acoustic channels. Consequently, for leak location, the pipe length is no longer a prerequisite. The practical location results show the validness of the proposed scheme.

Performance Enhancement by Local Strain in Channel n-Channel Metal–Oxide–Semiconductor Field-Effect Transistors on (111) Substrate

In this study, an n-channel metal–oxide–semiconductor field-effect transistor (nMOSFET) fabricated with local strained channel techniques on a (111) Si substrate using a SiN capping layer with high mechanical stress and the stack gate of amorphous silicon (α-Si) and polycrystalline silicon (poly-Si) was investigated. By using these techniques, the performance improvement of the nMOSFETs in the <110> channel direction on the (111) substrate was achieved. The on-current and transconductance (Gm) increased with increasing SiN capping layer or α-Si layer thickness. Our experimental results show that devices with a 700 Å α-Si layer show a 6.7% on-current improvement percentage relative to those with a 200 Å α-Si layer, and a corresponding Gm improvement percentage of 10.2%. In addition, charge pumping current/interface state density decreased for the samples with a thicker SiN layer.

Performance Analysis of a Pre-BLAST-DFE Technique for MISO Channels With Decentralized Receivers

The performance of a pre-Bell Laboratories Layered Space-Time Architecture (BLAST)-decision feedback equalization (DFE) technique with Tomlinson-Harashima precoding and decentralized receivers, operating over multiple-input single-output (MISO) frequency-selective fading channels, is evaluated. First, we derive the probability of symbol error for Tomlinson-Harashima precoding operating over single-input single-output channels with intersymbol interference. We then generalize this result to MISO frequency-selective fading channels with decentralized receivers by using the QR decomposition technique. The effect of optimal ordering of the decentralized receivers, which minimizes the total transmit energy, is investigated. We obtain a closed-form expression for the probability density function of the squared diagonal elements of the upper right triangular matrix belonging to the optimal QR decomposition when two transmit antennas and two receivers are used. We also provide simulations to corroborate the analytical results.

LDPC Code Design for Nonuniform Power-Line Channels

We investigate low-density parity-check code design for discrete multitone channels over power lines. Discrete multitone channels are well modeled as nonuniform channels, that is, different bits experience various channel parameters. We propose a coding system for discrete multitone channels that allows for using a single code over a nonuniform channel. The number of code parameters for the proposed system is much greater than the number of code parameters in conventional channel. Therefore, search-based optimization methods are impractical. We first formulate the problem of optimizing the rate of an irregular low-density parity-check code, with guaranteed convergence over a general nonuniform channel, as an iterative linear programming which is significantly more efficient than search-based methods. Then we use this technique for a typical power-line channel. The methodology of this paper is directly applicable to all decoding algorithms for which a density evolution analysis is possible.