Two-step Research Articles

A Null-Space Method for the Phase Unwrapping of Multitemporal SAR Interferometric Stacks

Multitemporal differential interferometric synthetic aperture radar analysis is of fundamental importance in the monitoring of Earth surface displacements. In this context, a key role for the reconstruction of the deformation maps and time series is played by the phase unwrapping (PhU) that reconstructs the unrestricted phase signals starting from the measured wrapped versions, i.e., the interferograms. PhU is typically carried out independently for each interferogram in the 2-D azimuth-range domain via the efficient minimum cost flow (MCF) optimization technique. Recently, it has been proposed a two-step (TS) strategy that exploits both the temporal and the spatial structures of the available interferograms. The MCF algorithm is applied in this case also in the temporal/spatial baseline domain, and this step is combined with the classical 2-D space unwrapping. However, the restriction on the use of the MCF algorithm in the baseline domain poses limitations on the interferogram generation scheme. We present a formulation which makes use of the overdetermined nature of the operator that relates the phase differences to the absolute phase values: the problem is addressed in a more general framework that can cope with the 3-D (2-D space and time) nature of the data. This formulation is derived with reference to the sequential (TS) approach to overcome its restrictions on the interferogram generation. The new algorithm is validated on both simulated and real data. Moreover, the use of this new formulation for a full 3-D unwrapping is also addressed.

A New Post-filter Algorithm Combined with Two-step Adaptive Beamformer

The optimal microphone array, in the sense of minimum mean square errors (MMSE), includes two processing blocks: the minimum variance distortionless response (MVDR) beamformer and the single-channel Wiener filter, which acts as post-filter. In this paper, we propose a new post-filter algorithm based on assumptions that both the noise power attenuation factor (NPAF) and signal power attenuation factor (SPAF) are time invariant in the reverberant room. The algorithm recursively estimates both factors from available measurements and uses them in estimation of the post-filter parameters. Additionally, to overcome the problem of the poor performance of the MVDR beamformer in reverberant conditions, we propose the usage of the two-step (TS) MVDR algorithm. This algorithm improves the robustness of the beamformer and its ability to suppress the interferences using an estimate of the desired speaker transfer function. Although TS MVDR beamformer and proposed post-filter can work separately, or combined with other algorithms, the best performance is obtained when they work together. The performance of the proposed combination of new post-filter algorithm and TS MVDR beamformer is tested in a simulated reverberant room and compared with similar algorithms, which gave rather good results.

A comparison of the shear-peel and third-order bond strengths of orthodontic brackets with 2 etch techniques and the role of bracket asymmetry

Innovations in orthodontic bonding are inevitably followed by a flurry of studies to ascertain efficacy. Unfortunately, the published reports are often contradictory or highly variable. The primary purpose of this study was to analyze protocols that measure orthodontic bracket bond strength. The effects of loading mode and the role of bracket asymmetry were examined. The secondary goal was to test a self-etch enamel preparation system. Flattened stainless steel orthodontic brackets (.022-in Victory Series, 3M Unitek, Monrovia, Calif) were bonded to a total of 192 flattened bovine incisors with a resin composite bonding agent (Transbond XT, 3M Unitek.) The enamel was prepared with traditional, two-step (TS) acid (37% phosphoric acid gel) etching and priming (Transbond XT Primer, 3M Unitek) or with a single step (SS) self-etch (Transbond Plus, 3M Unitek) material. Cement thickness was held constant and bonding was done under controlled temperature and humidity. The brackets were debonded in the occlusogingival and in the gingivocclusal directions (ie, the 2 senses of shear-peel) and using a new technique in the buccal-root and in the lingual-root directions (ie, the 2 senses of a third-order moment.) Data showed no significant differences between TS and SS regardless of load modality. However, significant differences were revealed between the senses of debonding, indicating bracket asymmetry effects. The wide clinical use of these newer self-etching primers has been supported by these limited findings. A new third-order debonding protocol has been demonstrated to be a useful tool. Bracket asymmetry affects some bond strength values, and there is a need for standardization of testing protocols.

Intensity-modulated radiotherapy of breast cancer using direct aperture optimization

Background and purpose To design a clinically reliable and efficient step-and-shoot IMRT delivery technique for the treatment of breast cancer using direct aperture optimization (DAO). Using DAO, segments are created and optimized within the same optimization process. Patients and methods The DAO technique implemented in the Pinnacle treatment planning system, which is called direct machine parameter optimization (DMPO), was used to generate IMRT plans for twelve breast cancer patients. The prescribed dose was 50 Gy. Two DMPO plans were generated. The first approach uses DMPO only; the second technique combines DMPO with two predefined segments (DMPO segm), having shapes identical to the conventional tangential fields. The weight of these predefined segments is optimized simultaneously with DMPO. The DMPO plans were compared with normal two-step (TS) IMRT, creating segments after optimizing the intensity. Results Dose homogeneity within the target volume was 4.8±0.6, 4.3±0.5 and 3.8±0.5 Gy for the TS, DMPO and DMPO segm plans, respectively. Comparing the IMRT plans with an idealized dose distribution obtained using only beamlet optimization, the degradation of the dose distribution was less for the DMPO plans compared with the two-step IMRT approach. Furthermore, this degradation was similar for all patients, while for the two-step IMRT approach it was patient specific. Conclusions An efficient step-and-shoot IMRT solution was developed for the treatment of breast cancer using DMPO combined with two predefined segments.

Resonant X-ray Raman scattering from dense gases and solutions

To complement conventional theory of resonant X-ray Raman scattering (RXS) adapted either for rarefied gases or solids, we propose a theory and corresponding analysis for RXS from dense gases and solutions. We show that the dephasing broadening of the spectral lines due to interaction with buffer or solvent particles qualitatively changes the physics of the X-ray scattering. The dephasing results in an additional, two-step (TS) scattering, contribution to the RXS cross-section, which interferes with the Raman one-step (OS) channel and which shows a nondispersive behaviour. This results in a doubling of the spectral lines by detuning the excitation frequency away from resonance. The theory is demonstrated numerically for RXS of formaldehyde in solution.

Laparoscopic gastric banding with Lap-Band for morbid obesity: two-step technique may improve outcome.

Laparoscopic placement of an adjustable gastric band is an attractive alternative for patients who can benefit from a restrictive bariatric procedure. Creation of the retrogastric tunnel (RGT) may, however, be a considerable challenge early in the surgeon's learning curve. Recent reports described up to 10% band slippage and occasional gastric perforation associated with RGT. The two-step (TS) technique involves a crural dissection towards the angle of His through a gastrohepatic ligament approach. It facilitates passage of the band's tubing posteriorly with no wide posterior gastric wall dissection. Prospective data were registered for the 109 patients (92 females, 17 males) who underwent laparoscopic adjustable gastric banding from December 1998 to May 2000. In 11 patients the standard RGT approach was used, and in 98, the TS technique. The two groups were demographically similar. Mean age was 37 years (18-59); mean preoperative weight was 120 kg (90-165). All procedures were completed laparoscopically. The mean operative time was 59 minutes (31-150) and the mean hospital stay 1.2 days (1-5). Complications in the TS group were gastric wall hematoma in one patient, 3 days of intubation postoperatively in one patient, damage to a band demonstrated in a postoperative contrast study in one patient, and a port-site hernia in one patient. There was no band slippage in the TS group. Among the 11 patients undergoing RGT, there was band slippage in three (27%), immediately postoperatively in one and after 3 and 11 months in the other two. In a mean follow-up of 7 months (1-18), similar weight loss was found in both groups. The mean BMI decreased from 44 kg/m2 (36-61) preoperatively to 40, 38, 36, 34 kg/m2 at 1, 3, 6 and 9 months respectively. 52 patients required band adjustment; of these, 12 required two adjustments. Our experience with both the RGT and TS techniques indicates that the latter may offer better results, particularly in the early experience period. It is recommended that in their initial experience with the adjustable band, surgeons should become familiar with this approach.

Double ionization of atomic helium under heavy ion impact

Cross sections for double ionization of helium by multiply-charged ion impact and the corresponding ratios of double-to-single ionization are presented as a sum of the contributions given by the one-step (shake-off) and two-step (TS) processes. An analytic form is found for the continuum wavefunction which is valid in both limiting cases of low and high velocities of the relative motion. Using this wavefunction, the TS cross sections are calculated within the independent-event model. The results for the ratios of double-to-single ionization show satisfactory agreement with the experimental data available.

STEROIDS. LV.1 STEROIDAL SAPOGENINS. XXXV.2 CHEMICAL INTRODUCTION OF THE 6β-HYDROXY GROUP INTO STEROIDAL Δ4-3-KETONES BY A TWO STEP SEQUENCE

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSTEROIDS. LV.1 STEROIDAL SAPOGENINS. XXXV.2 CHEMICAL INTRODUCTION OF THE 6β-HYDROXY GROUP INTO STEROIDAL Δ4-3-KETONES BY A TWO STEP SEQUENCEJ. ROMO, G. ROSENKRANZ, CARL DJERASSI, and FRANZ SONDHEIMERCite this: J. Org. Chem. 1954, 19, 9, 1509–1515Publication Date (Print):September 1, 1954Publication History Published online1 May 2002Published inissue 1 September 1954https://doi.org/10.1021/jo01374a015RIGHTS & PERMISSIONSArticle Views267Altmetric-Citations27LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (517 KB) Get e-Alerts Get e-Alerts

REVERSIBLE TWO STEP OXIDATION

In general, an organic dye stuff of quinoid structure is reduced by accepting from the reducing agent two hydrogen atoms or two electrons at once. Until recently no case had been known in which the reduction would occur in two separate steps in succession, each involving the acceptance of one electron (or hydrogen atom). This experience seemed to be quite natural and in agreement with the customary formulae, used in organic chemistry, for a quinoid or a benzoid compound. No intermediary form seemed to be imaginable, because one valence in this imaginary “semiquinoid” form would have to stand aloof and unsaturated: