Compensation of Thermal Effects by Dynamic Bias in Low Noise Amplifiers

There is an increasing need to understand how thermal effects affect the performance of amplifiers in radar systems. Increased chip power densities are to be expected as the integration of multiple transceivers in SiGe/BiCMOS and in GaN, increases. This will increase the electrical as well as thermal coupling between the transceivers, and the increased temperature is likely to impair the performance of amplifiers. Dynamic bias techniques are used today to increase the efficiency of transmitters. Therefore, it is important to investigate if these techniques can be used also to compensate for thermal effects which affect the elements in a multi transceiver chip. This thesis deals with the development of a GaN based temperature sensor as well as a study of the heat propagation properties in GaN on SiC structures. Furthermore, a study of thermal effects in low noise amplifiers has been carried out, and the use of dynamic bias to compensate for thermal performance deterioration, as well as other features, is demonstrated. A mesa resistor sensor and Schottky diode sensor were designed and evaluated. It was shown that a 15 μm mesa resistor works well as a temperature sensor when biased at an appropriate point. Models for predicting the temperature were developed based on measurements and a calibration method is proposed. It was shown that heat pulses can be detected by the sensors. A sensor area was designed and used to study heat propagation versus distance and temperature. A model describing the response of the sensor was proposed and evaluated. The model was used to study how heat is coupled to the sensor in the GaN and SiC layers. The thermal conductivity was seen to increase significantly in the GaN and SiC layers at lower temperatures. The layer time constants and propagation delay were observed to increase with temperature and distance. Light sources were also observed to impact the sensor current response. It was determined by measurements that thermal effects in general degrades the performance of three evaluated low noise amplifiers, and that dynamic bias control techniques can be used to cancel these effects for certain parameters. Increased power consumption levels was observed when applying dynamic bias control. In addition, it was demonstrated how dynamic bias can be used to eliminate gain recovery effects after high power pulses. Lastly, suggestions for different modes of operation, where dynamic bias is utilized differently, are presented

Characterization and Compensation of Thermal Effects in GaN HEMT Technologies

Further advancements with GaN based technologies relies on the ability to handle the heat flux, which consequently arises from the high power density. Advanced cooling techniques and thermal optimization of the technology are therefore prioritized research areas. Characterization techniques play a key role in the development of new cooling solutions, since these rely on accurate measurements of e.g. the temperature of the device. This thesis covers techniques to electrically characterize the lateral and vertical heat properties in GaN, and a temperature compensation technique for GaN MMICs.The first part outlines a methodology to electrically extract the thermal resistance of a GaN resistor without risking distortion from field induced electron trapping effects, which are exhibited by GaN heterostructures. The technique uses differential resistance measurements to identify a suitable resistor geometry, which minimizes trapping effects while enhancing the self-heating. Such conditions are crucial for electrical methods since these exploit the self- heating for a thermal analysis.Furthermore, a test structure and measurement method to electrically characterize the lateral heat spread was designed and evaluated. The structure is implemented with a thermal sensor, which utilizes the temperature-dependent IV characteristics of a GaN resistor, making it suitable for integration in GaN MMICs. The transient response can be obtained to extract the thermal time constants and propagation delay of the heat spread. At higher ambient temperatures, the propagation delay increases and the thermal coupling is increased. Lastly, a biasing technique to compensate for thermal degradation of the RF performance of an LNA was developed. By utilizing the gate- and drain voltage dependence of the RF performance, a constant gain against increasing temperature can e.g. be achieved

The effective conductivity of arrays of squares: large random unit cells and extreme contrast ratios

An integral equation based scheme is presented for the fast and accurate computation of effective conductivities of two-component checkerboard-like composites with complicated unit cells at very high contrast ratios. The scheme extends recent work on multi-component checkerboards at medium contrast ratios. General improvement include the simplification of a long-range preconditioner, the use of a banded solver, and a more efficient placement of quadrature points. This, together with a reduction in the number of unknowns, allows for a substantial increase in achievable accuracy as well as in tractable system size. Results, accurate to at least nine digits, are obtained for random checkerboards with over a million squares in the unit cell at contrast ratio 10^6. Furthermore, the scheme is flexible enough to handle complex valued conductivities and, using a homotopy method, purely negative contrast ratios. Examples of the accurate computation of resonant spectra are given.Comment: 28 pages, 11 figures, submitted to J. Comput. Phy

Relational autonomy in the care of the vulnerable: health care professionals' reasoning in Moral Case Deliberation (MCD)

In Moral Case Deliberation (MCD), healthcare professionals discuss ethically difficult patient situations in their daily practice. There is a lack of knowledge regarding the content of MCD and there is a need to shed light on this ethical reflection in the midst of clinical practice. Thus, the aim of the study was to describe the content of healthcare professionals' moral reasoning during MCD. The design was qualitative and descriptive, and data consisted of 22 audio-recorded inter-professional MCDs, analysed with content analysis. The moral reasoning centred on how to strike the balance between personal convictions about what constitutes good care, and the perceived dissonant care preferences held by the patient. The healthcare professionals deliberated about good care in relation to demands considered to be unrealistic, justifications for influencing the patient, the incapacitated patient's nebulous interests, and coping with the conflict between using coercion to achieve good while protecting human dignity. Furthermore, as a basis for the reasoning, the healthcare professionals reflected on how to establish a responsible relationship with the vulnerable person. This comprised acknowledging the patient as a susceptible human being, protecting dignity and integrity, defining their own moral responsibility, and having patience to give the patient and family time to come to terms with illness and declining health. The profound struggle to respect the patient's autonomy in clinical practice can be understood through the concept of relational autonomy, to try to secure both patients' influence and at the same time take responsibility for their needs as vulnerable humans

The impact of direct admission to a catheterisation lab/CCU in patients with ST-elevation myocardial infarction on the delay to reperfusion and early risk of death: results of a systematic review including meta-analysis

BACKGROUND: For each hour of delay from fist medical contact until reperfusion in ST-elevation myocardial infarction (STEMI) there is a 10% increase in risk of death and heart failure. The aim of this review is to describe the impact of the direct admission of patients with STEMI to a Catheterisation laboratory (cath lab) as compared with transport to the emergency department (ED) with regard to delays and outcome. METHODS: Databases were searched for from April-June 2012 and updated January 2014: 1) Pubmed; 2) Embase; 3) Cochrane Library; 4) ProQuest Nursing and 5) Allied Health Sources. The search was restricted to studies in English, Swedish, Danish and Norwegian languages. The intervention was a protocol-based clinical pre-hospital pathway and main outcome measurements were the delay to balloon inflation and hospital mortality. RESULTS: Median delay from door to balloon was significantly shorter in the intervention group in all 5 studies reported. Difference in median delay varied between 16 minutes and 47 minutes. In all 7 included studies the time from symptom onset or first medical contact to balloon time was significantly shorter in the intervention group. The difference in median delay varied between 15 minutes and 1 hour and 35 minutes. Only two studies described hospital mortality. When combined the risk of death was reduced by 37%. CONCLUSION: An overview of available studies of the impact of a protocol-based pre-hospital clinical pathway with direct admission to a cath lab as compared with the standard transport to the ED in ST-elevation AMI suggests the following. The delay to the start of revascularisation will be reduced. The clinical benefit is not clearly evidence based. However, the documented association between system delay and outcome defends the use of the pathway. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s13049-014-0067-x) contains supplementary material, which is available to authorized users

Suspicion and treatment of severe sepsis. An overview of the prehospital chain of care

Sepsis is a life-threatening condition where the risk of death has been reported to be even higher than that associated with the major complications of atherosclerosis, i.e. myocardial infarction and stroke. In all three conditions, early treatment could limit organ dysfunction and thereby improve the prognosis

Evaluation of health services and treatment alliance among extensively hospitalized patients due to severe self-harm–results from the Extreme Challenges project

Background - Extensive psychiatric hospitalization due to repeated severe self-harm (SH), is a poorly researched area, but a challenge within health services (HS). Recent studies have demonstrated high levels of involuntary treatment among patients with severe personality disorder (PD) and complex comorbidity. Keeping focus on extensively hospitalized SH patients, this study aimed to investigate patients’ and clinicians’ evaluation of HS and treatment alliance. Method - A cross-sectional study with an inpatient sample (age >18 years) with frequent (>5) or long (>4 weeks) psychiatric hospital admissions last year due to SH or SA recruited from 12 hospitals across health regions (N = 42). Evaluation included patient and clinician report. Results - A minority of the patients (14%) were satisfied with HS before the current admission, 45% (patients) and 20% (clinicians) found the current admission helpful, and 46% (patients) and 14% (clinicians) worried about discharge. Treatment complaints were received in 38% of the cases. Outpatient mental HS were available after discharge for 68% and a majority of clinicians indicated satisfactory contact across HS. More intensive or specialized formats were unusual (structured outpatient treatment 35%, day treatment 21%, ambulatory services 32%, planned inpatient services 31%). Mutual problem understanding, aims, and confidence in therapists during the hospital stay were limited (patient-rated satisfactory mutual problem understanding: 39%, aims of stay: 50%, confidence: 50%). Patient and therapist alliance-ratings were in concordance for the majority. Conclusion - The study highlights poor HS satisfaction, poor patient–therapist coherence, limited treatment alliance and limited follow-up in structured treatments addressing SH or intermediary supportive ambulatory/day/inpatient services

Lineage 2 West Nile Virus as Cause of Fatal Neurologic Disease in Horses, South Africa

Lineage 2 WNV may be missed as a cause of neurologic infections in horses and humans in this region

GRB 020410: A Gamma-Ray Burst Afterglow Discovered by its Supernova Light

We present the discovery and monitoring of the optical transient (OT) associated with GRB 020410. The fading OT was found by Hubble Space Telescope (HST) observations taken 28 and 65 days after burst at a position consistent with the X-ray afterglow. Subsequent re-examination of early ground based observations revealed that a faint OT was present 6 hours after burst, confirming the source association with GRB 020410. A deep non-detection after one week requires that the OT re-brightened between day 7 and day 28, and further late time HST data taken approximately 100 days after burst imply that it is very red.We compare both the flux and color of the excess with supernova models and show that the data are best explained by the presence of a Type Ib/c supernova at a redshift z ~ 0.5, which occured roughly coincident with the day of GRB.Comment: 23 Pages, 9 figures, submitted to Ap