Textured Ion-Beam Assisted Deposition: Magnesium Oxide Template on Non-Metallic Flexible Ceraflex for Epitaxial Growth of Perovskite Films

This paper reports on a systematic study of the development of bi-axially textured magnesium oxide (MgO) templates on flexible ceramic polycrystalline ceraflex substrates by ion-beam assisted deposition (IBAD) and the preliminary test of the growth of YBa₂Cu₃O₇ on top. The rough surface of the original ceraflex, with a typical roughness of about 100 nm, presented a serious challenge in the development of textured IBAD-MgO. By a coating of multiple layers of spin-on-glass (SOG), the surface roughness has been reduced to about a few nanometers. After an amorphous Y₂O₃ buffer had been deposited on multilayer SOG coated ceraflex, IBAD-MgO and homo-epitaxial MgO were grown with good in-plane texture of Δ ∼ 9.3° An epitaxial SrTiO₃ film was subsequently deposited on this textured template with in-plane Δ ∼ 10.8° Finally, an epitaxial YBa₂Cu₃O₇ superconducting film was grown on LaMnO₃ buffered and IBAD-MgO textured ceraflex, and AC susceptibility examination indicated the transition temperature was 88 K. The results have demonstrated that an IBAD-MgO textured template on ceraflex can be used for the epitaxial growth of perovskite films.     

Rapid preparation of smooth nanocellulose films using spray coating

Spraying of nanocellulose (NC) on a solid surface to prepare films is an alternative technique to vacuum filtration, which requires a long drainage time and produces films which can sometimes be difficult to separate from the filter. This letter reports a rapid preparation technique for nano-cellulose films using a bench scale system spray coating nanocellulose suspension onto stainless steel plates. After spraying NC suspension onto a smooth steel plate travelling on a constant velocity conveyor, the films can be dried directly on the plates using standard laboratory procedures, saving processing time and effort. By adjusting the suspension consistency, we were able to reproducibly make films with a basis weight ranging from 52.8 ± 7.4 to 193.1 ± 3.4 g/m² when spraying on to a plate moving at a velocity of 0.32 cm/s. The operator preparation time for the nanocellulose film was 1 min, independent of the sample basis weight, which compares to production times reported in the literature of 10 min using filtration techniques. The films made by spray coating showed higher thickness, but comparable uniformity, to those made by vacuum filtration. Optical profilometry measurements showed that over a 1 cm × 1 cm inspection area that the surface roughness (RMS) of the NC film is only 389 nm on the spray coated side in contact with the steel plates, compared to 2087 nm on the outside surface. Thus, the reduction in preparation time for producing the nanocellulose film recommends this spray coating technique as a rapid and flexible method to produce NC films at the laboratory scale.     

Development of Injectable Biodegradable Multi-Arms PEG-Based Hydrogels: Swelling and Degradation Investigations

Summary : Injectable biodegradable hydrogels have been developed to determine the efficacy of biomaterials for the treatment of periodontitis through control delivery of bone-healing bioactives. The hydrogels were prepared from the PEG-ylated macromer of Boltorn™ H20 (BH20) and an acrylated triblock copolymer of polylactide-polyethylene glycol (2k)-polylactide (PLA) in various molar ratios using ammonium persulfate and sodium ascorbate as a free radical initiating system. Preliminary investigations involving the synthesis of PLA hydrogels with different PLLA block lengths were studied in order to determine the swelling ratios and degradation rates of the biodegradable component of the hydrogels prior to copolymerization with BH20. The swelling and degradation studies of PLA with PEG diacrylate (FW 700) hydrogels were established in phosphate buffered saline (PBS) at 37 °C, pH 7.4 and in water (pH ∼5.5). They have been shown to have low swelling ratios (Q_max = 4.4 to 3.6) and degradation times of 20–30 days. The swelling and degradation parameters were found to be dependent on the molar ratio of the PEG diacrylate to PLA in the copolymer.     

Thermal infrared lines of methane broadened by nitrogen at low temperatures

Measurements of spectral transmittance in the v₄-fundamental band of ¹²CH₄ have been performed at low temperatures using a Fourier transform spectrometer with apodized spectral resolution of 0.06 cm^-1. With applications to lines formed in the atmospheres of Titan and Earth in mind, N₂ has been used as the broadening gas. Comparisons of observed and computed spectral transmittances on a line-by-line basis have yielded line strengths, N₂-broadened half-widths and their variation with temperature. Best agreement between measured and computed spectra was obtained when the absolute intensity of the band was taken as 128 cm^-2-atm^-1 at 296 K. Line widths were found to vary as Tⁿ with n = -1.0 for lines of the F-species and 0.63 for the A-species. Our measured line widths are considerably larger than those used in the AFGL compilation.     

Blind multiuser detection over highly dispersive CDMA channels

This paper addresses blind multiuser detection in a direct-sequence code-division multiple-access (DS-CDMA) network in presence of both multiple-access interference and intersymbol interference. In particular, it considers a DS-CDMA system where K out of N users are transmitting; the N admissible spreading codes are known, and so is the code of the user to be demodulated. The number of interferers, the signatures of a certain number, possibly all, of the interferers, and the channel impulse response of each active user are unknown. The spreading codes of the unknown interferers are determined via a procedure that exploits the knowledge of the set of admissible transmitted codes and of the known active codes. The procedure applies to both single and multiple receiving antennas. The performance assessment of a blind decorrelating detector, implemented by resorting to the proposed identification procedure, shows that it outperforms a plain subspace-based blind decorrelator for small sizes of the estimation sample.     

Signal Design for Bandwidth Efficient Multiple Access under Asymptotic Effective Energy Constraints

The problem of signal design for bandwidth-efficient multiple access (BEMA) over additive white Gaussian noise (AWGN) channels is addressed under quality of service (QoS) requirements specified by asymptotic effective energies (AEEs). The AEE characterizes the bit error rate (BER) in the low-noise regime, but in contrast to BER, it is tractable and amenable to analysis and signal design. We adopt the BEMA strategy of bandwidth conservation where users are detected successively using minimum mean-squared error decision feedback (MMSE-DF) detection and where signals are designed in a greedy fashion for one user at a time, in the reverse order in which the users are detected. The signal design method proposed here is based on an exact characterization of how a signal update for one user affects the issue of preserving bandwidth with the addition of signals for subsequent users. A geometric insight in the construction of good signal sets and significant improvements in bandwidth over full-rank or orthogonal signaling are obtained. The main result of this paper can hence be seen as providing a tight upper bound on the minimum signature sequence dimension or rank (and hence bandwidth) needed to satisfy individual, possibly distinct user QoS constraints specified in terms of the AEE measure.     

Optimum receivers and low-dimensional spreaded modulation for multiuser space-time communications

The jointly optimum receiver is obtained for multi- user communications in a frequency nonselective Rayleigh-fading channel with N/sub T/ transmit antennas per user and N/sub R/ receive antennas. Based on a general analysis of quadratic receivers in zero-mean complex Gaussian vectors, asymptotically tight expressions (for high signal-to-noise ratio (SNR)) for the pairwise error probabilities are derived. Subsequently, it is shown that N/sub T/-dimensional single-user signaling suffices to provide full diversity order N=N/sub T/N/sub R/ for all the users. In other words, the presence of other users does not increase the minimum dimension required beyond what is needed for the single-user space-time channel. For the special case of low-rank "code-division multiple-access (CDMA)" signaling with N/sub T/=1 and provided the signatures of any two users are linearly independent, it is shown that the error probability of a K-user system asymptotically approaches single-user-like performance for every user. Remarkably, therefore, an increase in the number of users, and hence an increase in the aggregate spectral efficiency, does not require the users to transmit with more power to achieve single-user-like performance asymptotically. A signal design algorithm is proposed to illustrate this point and examples are given. These results are then generalized to the multiple transmit antenna case. A new (N/sub T/+1)-dimensional signaling strategy is proposed for the multiuser channel that leverages existing single-user space-time signal designs while ensuring full diversity order and single-user-like performance asymptotically for every user.     

Superior non-woven sheet forming characteristics of low-density cationic polymer-cellulose nanofibre colloids

This work examines the addition of cationic polymers, cationic polyacrylamide (CPAM) and polyamide–amine–epichlorohydrin (PAE), to cellulose nanofibres to produce superior forming characteristics. The addition of 2 mg of high MW CPAM/g of nanofibres halved the drainage time to under 1 min at 0.1 wt% solids content due to increasing the floc size and the fibre forming a bulky and porous filter medium during drainage. The more open structure created in the wet state was partially preserved during the drying process, reducing the sheet density from 760 to 680 kg/m³, at the highest level of polymer addition. The addition of CPAM resulted in significant additional bridging between nanofibres, which then substantially increased the non-uniformity of the filter medium. PAE addition at 10 mg/g of micro fibrillated cellulose (MFC), also reduced drainage time, while increasing retention, but without changing the sheet uniformity. Wet strength increased continuously with PAE addition level, reaching 31.6 kN m/kg at the highest level of 20 mg of PAE/g of MFC.     

An algebraic family of complex lattices for fading channels with application to space-time codes

A new approach is presented for the design of full modulation diversity (FMD) complex lattices for the Rayleigh-fading channel. The FMD lattice design problem essentially consists of maximizing a parameter called the normalized minimum product distance d/sub p//sup 2/ of the finite signal set carved out of the lattice. We approach the problem of maximizing d/sub p//sup 2/ by minimizing the average energy of the signal constellation obtained from a new family of FMD lattices. The unnormalized minimum product distance for every lattice in the proposed family is lower-bounded by a nonzero constant. Minimizing the average energy of the signal set translates to minimizing the Frobenius norm of the generator matrices within the proposed family. The two strategies proposed for the Frobenius norm reduction are based on the concepts of successive minima (SM) and basis reduction of an equivalent real lattice. The lattice constructions in this paper provide significantly larger normalized minimum product distances compared to the existing lattices in certain dimensions. The proposed construction is general and works for any dimension as long as a list of number fields of the same degree is available.     

Leveraging coherent space-time codes for noncoherent communication via training

Training codes are introduced for the multiple-antenna, noncoherent, multiple block-Rayleigh-fading channel in which the fading coefficients, which are constant over a fixed number of dimensions (coherence interval) for each block and then change independently to a new realization, are known neither at the transmitter nor at the receiver. Each codeword of a training code consists of a part known to the receiver-used to form a minimum mean-squared error (MMSE) estimate of the channel-and a part that contains codeword(s) of a space-time block or trellis code designed for the coherent channel (in which the receiver has perfect knowledge of the channel). The channel estimate is used as if it were error-free for decoding the information-bearing part of the training codeword. Training codes are hence easily designed to have high rate and low decoding complexity by choosing the underlying coherent code to have high rate and to be efficiently decodable. Conditions for which the estimator-detector (E-D) receiver is equivalent to the optimal noncoherent receiver are established. A key performance analysis result of this paper is that the training codes when decoded with the E-D receiver achieve a diversity order of the error probability that is equal to the diversity order of the underlying coherent code. In some cases, the performance of training codes can be measured relative to coherent reception via "training efficiency," which is then optimized over the energy allocation between the training and data phases. In the limit of increasing block lengths, training codes always achieve the performance of coherent reception. The examples of training codes provided in this work have polynomial complexity in rate but an error rate comparable to the best performing unitary designs available, even though the latter require exponential decoding complexity.