A 43-GHz AlInAs/GaInAs/InP HEMT grid oscillator

A 36-element hybrid grid oscillator has been fabricated. The active devices are InP-based High Electron Mobility Transistors (HEMT's). The grid oscillates at 43 GHz with an effective radiated power of 200 mW. Measurements show the E and H-plane radiation patterns have side lobes 10 dB below the main beam. These results are a significant improvement over a previous millimeter-wave grid oscillator, which had a divided beam because of substrate mode

Modelling of quasi-optical arrays

A model for analyzing quasi-optical grid amplifiers based on a finite-element electromagnetic simulator is presented. This model is deduced from the simulation of the whole unit cell and takes into account mutual coupling effects. By using this model, the gain of a 10×10 grid amplifier has been accurately predicted. To further test the validity of the model three passive structures with different loads have been fabricated and tested using a new focused-beam network analyzer that we developed

Transcatheter Versus Surgical Aortic Valve Replacement in Young, Low-risk Patients with Severe Aortic Stenosis

Aortic stenosis is a common form of acquired degenerative valvular disease associated with poor survival after the onset of symptoms. Treatment options for patients with aortic stenosis in addition to medical therapy include surgical aortic valve replacement (SAVR) with either tissue or mechanical valves, or transcatheter aortic valve replacement (TAVR) with either balloon-expandable or self-expanding valves via either transfemoral or alternative access routes. In this review, the authors discuss the current evidence and special considerations regarding the use of TAVR versus SAVR in the management of severe aortic stenosis in young (<65 years of age), low-risk patients, highlighting the history of aortic stenosis treatment, the current guidelines and recommendations, and important issues that remain to be addressed. Ultimately, until ongoing clinical trials with long-term follow-up data shed light on whether interventions for aortic stenosis can be broadened to a low-risk population, TAVR in young, low-risk patients should be undertaken with caution and with guidance from a multidisciplinary heart team

Homograft use in reoperative aortic root and proximal aortic surgery for endocarditis: A 12-year experience in high-risk patients

ObjectivesWe examined the early and midterm outcomes of homograft use in reoperative aortic root and proximal aortic surgery for endocarditis and estimated the associated risk of postoperative reinfection.MethodsFrom January 2001 to January 2014, 355 consecutive patients underwent reoperation of the proximal thoracic aorta. Thirty-nine patients (10.9%; mean age, 55.4 ± 13.3 years) presented with active endocarditis; 30 (76.9%) had prosthetic aortic root infection with or without concomitant ascending and arch graft infection, and 9 (23.1%) had proximal ascending aortic graft infection with or without aortic valve involvement. Sixteen patients (41.0%) had genetically triggered thoracic aortic disease. Twelve patients (30.8%) had more than 1 prior sternotomy (mean, 2.4 ± 0.6).ResultsValved homografts were used to replace the aortic root in 29 patients (74.4%); nonvalved homografts were used to replace the ascending aorta in 10 patients (25.6%). Twenty-five patients (64.1%) required concomitant proximal arch replacement with a homograft, and 2 patients (5.1%) required a total arch homograft. Median cardiopulmonary bypass, cardiac ischemia, and circulatory arrest times were 186 (137-253) minutes, 113 (59-151) minutes, and 28 (16-81) minutes. Operative mortality was 10.3% (n = 4). The rate of permanent stroke was 2.6% (n = 1); 3 additional patients had transient neurologic events. One patient (1/35, 2.9%) returned with aortic valve stenosis 10 years after the homograft operation. During the follow-up period (median, 2.5 years; range, 1 month to 12.3 years), no reinfection was reported, and survival was 65.7%.ConclusionsThis is one of the largest North American single-center series of homograft use in reoperations on the proximal thoracic aorta to treat active endocarditis. In this high-risk population, homograft tissue can be used with acceptable early and midterm survival and a low risk of reinfection. When necessary, homograft tissue may be extended into the distal ascending and transverse aortic arch, with excellent results. These patients require long-term surveillance for both infection and implant durability

Portal vein thrombosis following laparoscopic cholecystectomy complicated by dengue viral infection: a case report

<p>Abstract</p> <p>Introduction</p> <p>Portal vein thrombosis is an uncommon post-operative complication following abdominal surgery. Although therapeutic anticoagulation is recommended, this treatment may be questionable when the patient has an associated bleeding diathesis.</p> <p>Case presentation</p> <p>We report a case of a 63-year-old woman of Asian Indian ethnicity who developed portal vein thrombosis following an uneventful laparoscopic cholecystectomy for symptomatic gallstones. Her condition was further complicated by dengue viral infection in the post-operative period, with thrombocytopenia immediately preceding the diagnosis of portal vein thrombosis. The etiological connections between dengue viral infection with thrombocytopenia, laparoscopic cholecystectomy, portal vein thrombosis as well as the treatment dilemmas posed in treating a patient with portal vein thrombosis with a bleeding diathesis are discussed.</p> <p>Conclusion</p> <p>When portal vein thrombosis occurs in patients with contraindications to anticoagulation, there is a role for initial conservative management without aggressive anticoagulation therapy and such patients must be approached on an individualized basis.</p

Analysis and design for quasi-optical structures

Quasi-optical power combiners such as quasi-optical grids provide an efficient means of combining the output power of many solid-state devices in free space. Unlike traditional power combiners no transmission lines are used, therefore, high output powers with less loss can be achieved at higher frequencies. This thesis will detail three quasi-optical grids and their modeling. Two new models for analyzing quasi-optical grid amplifiers based on a finite-element simulator (HFSS) are presented and their validity is tested. A 36-element Ka-band grid amplifier is also described. The grid uses Flip-Chip InP HEMT's and has a peak gain of 4.8 dB at 36 GHz. A beam-steering method which includes microelectromechanical (MEM) switches on an insulating membrane is presented. The arrays are fabricated monolithically on highly- doped silicon by Rockwell Science Center. Processing challenges in fabricating the structures will be discussed. Measurements of s-parameters of capacitive arrays (Off state) are made and give promising results for the beam-steering grid. The design, construction and performance of a 36-element hybrid gid oscillator is also presented. The active devices are InP-based HEMT's. A locked frequency spectrum was achieved, with a Peak Effective Radiated Power (ERP) of 200 mW at 43 GHz. The grid is designed to minimize the substrate-mode power and produce an E-field with low side-lobes