Wide bandwidth high gain circularly polarized millimetre-wave rectangular dielectric resonator antenna

A wideband high gain circularly polarized (CP) rectangular dielectric resonator antenna (RDRA) having a frequency range of 21 to 31 GHz is proposed. The RDRA consists of two layers with different dielectric permittivities and has been excited using a cross slot aperture. The proposed antenna offers wide impedance and CP bandwidths of ~36.5% and 13.75% respectively, in conjunction with a high gain of ~12.5 dBi. Close agreement has been achieved between simulated and measured results

Wideband high-gain millimetre-wave three-layer hemispherical dielectric resonator antenna

A wideband high gain three-layer hemispherical dielectric resonator antenna (HDRA) that operates at TE511 and TE711 higher order modes is proposed. The HDRA is composed of three layers, which has permittivities of 20, 10 and 3.5. The multilayer structure has been chosen in order to reduce the Q-factor and achieve a wider impedance bandwidth. Cross slot feeding mechanism has been utilized taking into account the excited higher order modes for gain enhancement. The proposed antenna provides an impedance bandwidth of 35.8% over a frequency range of 20.8 to 29.9 GHz in conjunction with a high gain of ~9.5 dBi. The proposed DRA represents the first attempt in utilizing a mm-wave hemispherical DRA

Higher order mode circularly polarized two-layer rectangular dielectric resonator antenna

A two-layer higher order mode circularly polarized (CP) rectangular dielectric resonator antenna (RDRA) is proposed at a frequency range of 10 to 13GHz using a single-feed. The configuration incorporates the DRA and a dielectric coat layer with respective dielectric constants of 10 and 3.5. Utilizing the outer layer offers a number of advantages such as wider impedance and CP bandwidths of ∼21%, and 9.5%, respectively, as well as a high gain of ~11dBic. Close agreement has been achieved between experimental and simulated results

Higher order mode layered cylindrical dielectric resonator antenna

A wideband high gain circularly polarized layered cylindrical dielectric resonator antenna (DRA) that operates in a higher order mode is proposed in the X-band frequency range. The antenna consists of two dielectric layers having different dielectric constants and radii. The results demonstrate a considerably improved performance as a result of adding the outer dielectric layer, where wider impedance and axial ratio bandwidths have been attained in conjunction with a higher broadside gain of ~ 14 dBic. A prototype has been built and measured with close agreement between experimental and simulated results

Critical care usage after major gastrointestinal and liver surgery: a prospective, multicentre observational study

Background Patient selection for critical care admission must balance patient safety with optimal resource allocation. This study aimed to determine the relationship between critical care admission, and postoperative mortality after abdominal surgery. Methods This prespecified secondary analysis of a multicentre, prospective, observational study included consecutive patients enrolled in the DISCOVER study from UK and Republic of Ireland undergoing major gastrointestinal and liver surgery between October and December 2014. The primary outcome was 30-day mortality. Multivariate logistic regression was used to explore associations between critical care admission (planned and unplanned) and mortality, and inter-centre variation in critical care admission after emergency laparotomy. Results Of 4529 patients included, 37.8% (n=1713) underwent planned critical care admissions from theatre. Some 3.1% (n=86/2816) admitted to ward-level care subsequently underwent unplanned critical care admission. Overall 30-day mortality was 2.9% (n=133/4519), and the risk-adjusted association between 30-day mortality and critical care admission was higher in unplanned [odds ratio (OR): 8.65, 95% confidence interval (CI): 3.51–19.97) than planned admissions (OR: 2.32, 95% CI: 1.43–3.85). Some 26.7% of patients (n=1210/4529) underwent emergency laparotomies. After adjustment, 49.3% (95% CI: 46.8–51.9%, P<0.001) were predicted to have planned critical care admissions, with 7% (n=10/145) of centres outside the 95% CI. Conclusions After risk adjustment, no 30-day survival benefit was identified for either planned or unplanned postoperative admissions to critical care within this cohort. This likely represents appropriate admission of the highest-risk patients. Planned admissions in selected, intermediate-risk patients may present a strategy to mitigate the risk of unplanned admission. Substantial inter-centre variation exists in planned critical care admissions after emergency laparotomies

Body mass index and complications following major gastrointestinal surgery: A prospective, international cohort study and meta-analysis

Aim Previous studies reported conflicting evidence on the effects of obesity on outcomes after gastrointestinal surgery. The aims of this study were to explore the relationship of obesity with major postoperative complications in an international cohort and to present a metaanalysis of all available prospective data. Methods This prospective, multicentre study included adults undergoing both elective and emergency gastrointestinal resection, reversal of stoma or formation of stoma. The primary end-point was 30-day major complications (Clavien–Dindo Grades III–V). A systematic search was undertaken for studies assessing the relationship between obesity and major complications after gastrointestinal surgery. Individual patient meta-analysis was used to analyse pooled results. Results This study included 2519 patients across 127 centres, of whom 560 (22.2%) were obese. Unadjusted major complication rates were lower in obese vs normal weight patients (13.0% vs 16.2%, respectively), but this did not reach statistical significance (P = 0.863) on multivariate analysis for patients having surgery for either malignant or benign conditions. Individual patient meta-analysis demonstrated that obese patients undergoing surgery formalignancy were at increased risk of major complications (OR 2.10, 95% CI 1.49–2.96, P < 0.001), whereas obese patients undergoing surgery for benign indications were at decreased risk (OR 0.59, 95% CI 0.46–0.75, P < 0.001) compared to normal weight patients. Conclusions In our international data, obesity was not found to be associated with major complications following gastrointestinal surgery. Meta-analysis of available prospective data made a novel finding of obesity being associated with different outcomes depending on whether patients were undergoing surgery for benign or malignant disease