Secure wireless communication for hearing aids

Today, hearing aids communicate with a wide variety of devices via wireless connections. Like all networks, these connections are at risk of being compromised by an attacker when left unprotected. Until now, the partner company of this thesis, a large hearing instrument manufacturer, has used a proprietary security protocol to secure the connection. However, this company’s new generation of hearing aids will have more powerful hardware, which raises the question of using standardized security protocols anew. This paper aims to contribute to the clarification of this question. Since the bottleneck of communication overhead during data exchange will remain, this work focuses on the optimization of standardized security protocols with respect to this overhead. In a first phase, the theoretical foundations necessary for understanding the selected security protocols and overhead reduction are established. The security protocols are then weighed against each other with regard to a prototype, and TLS and TLS/QUIC are identified as the most promising. The implementing libraries chosen are wolfSSL for TLS and TLS/QUIC and lwIP for the underlying TCP/IP stack. Subsequently, the underlying transport framework for the TLS variant is implemented in a prototype and wolfSSL is tested in a client-server setup. The existing prototype, which also includes an interceptor task, can be used as a basis for further investigations. The use of the wolfSSL library has proven to be rather cumbersome, which is why its use in a further examination is not recommended.Heutzutage kommunizieren Hörgeräte mit den verschiedensten Geräten über drahtlose Verbindungen. Ungeschützt stehen diese Verbindungen, wie alle Netzwerke, in der Gefahr, von einem Angreifer kompromittiert zu werden. Bisher verwendete das Partnerunternehmen dieser Arbeit, ein grosser Hörgerät-Produzent, ein proprietäres Sicherheitsprotokoll, um die Verbindung abzusichern. Die neue Hörgerät- Generation dieser Firma wird aber über eine leistungsfähigere Hardware verfugen, was die Frage nach dem Einsatz von standardisierten Sicherheitsprotokollen neu aufwirft. Die vorliegende Arbeit will einen Beitrag dazu leisten, diese Frage zu klaren. Da das Nadelöhr des Kommunikations-Overheads während des Datenaustauschs bestehen bleiben wird, fokussiert diese Arbeit auf die Optimierung standardisierter Sicherheitsprotokolle betreffs dieses Overheads. Dafür werden in einer ersten Phase die theoretischen Grundlagen etabliert, die für das Verständnis der ausgewählten Sicherheitsprotokolle und der Overhead-Reduktion nötig sind. Für die Erstellung eines Prototyps werden dann die Sicherheitsprotokolle gegeneinander abgewogen und TLS und TLS/QUIC als die vielversprechendsten identifiziert. Als implementierende Bibliotheken werden wolfSSL für TLS und TLS/QUIC und lwIP für den darunterliegenden TCP/IP-Stack gewählt. Anschliessend wird das unterliegende Transport-Gerüst für die TLS-Variante in einem Prototypen umgesetzt und wolfSSL in einem Client-Server-Setup getestet. Der bestehende Prototyp, der auch eine Vorrichtung zum Abfangen von Paketen umfasst, kann als Grundlage für weitergehende Untersuchungen genutzt werden. Die Verwendung der wolfSSL-Bibliothek hat sich als eher umständlich erwiesen, weshalb von einem weiteren Einsatz abgeraten wird

Withholding or withdrawing invasive interventions may not accelerate time to death among dying ICU patients

We considered observational data available from the MIMIC-III open-access ICU database and collected within a study period between year 2002 up to 2011. If a patient had multiple admissions to the ICU during the 30 days before death, only the first stay was analyzed, leading to a final set of 6,436 unique ICU admissions during the study period. We tested two hypotheses: (i) administration of invasive intervention during the ICU stay immediately preceding end-of-life would decrease over the study time period and (ii) time-to-death from ICU admission would also decrease, due to the decrease in invasive intervention administration. To investigate the latter hypothesis, we performed a subgroups analysis by considering patients with lowest and highest severity. To do so, we stratified the patients based on their SAPS I scores, and we considered patients within the first and the third tertiles of the score. We then assessed differences in trends within these groups between years 2002-05 vs. 2008-11. Comparing the period 2002-2005 vs. 2008-2011, we found a reduction in endotracheal ventilation among patients who died within 30 days of ICU admission (120.8 vs. 68.5 hours for the lowest severity patients, p<0.001; 47.7 vs. 46.0 hours for the highest severity patients, p=0.004). This is explained in part by an increase in the use of non-invasive ventilation. Comparing the period 2002-2005 vs. 2008-2011, we found a reduction in the use of vasopressors and inotropes among patients with the lowest severity who died within 30 days of ICU admission (41.8 vs. 36.2 hours, p<0.001) but not among those with the highest severity. Despite a reduction in the use of invasive interventions, we did not find a reduction in the time to death between 2002-2005 vs. 2008-2011 (7.8 days vs. 8.2 days for the lowest severity patients, p=0.32; 2.1 days vs. 2.0 days for the highest severity patients, p=0.74)

Coupled free-carrier and exciton relaxation in optically excited semiconductors

The energy relaxation of coupled free-carrier and exciton populations in semiconductors after low-density ultrafast optical excitation is studied through a kinetic approach. The set of semiclassical Boltzmann equations, usually written for electron and hole populations only, is complemented by an additional equation for the exciton distribution. The equations are coupled by reaction terms describing phonon-mediated exciton binding and dissociation. All the other relevant scattering mechanisms, such as carrier-carrier, carrier-phonon, and exciton-phonon interactions, are also included. The resulting system of rate equations in reciprocal space is solved by an extended ensemble Monte Carlo method. As a first application, we show results for the dynamics of bulk GaAs in the range from 1 to ∼200 ps after photoexcitation. The build-up of an exciton population and its sensitivity to the excitation conditions are discussed in detail. As a consequence of the pronounced energy dependence of the LO-phonon-assisted transition probabilities between free-pair states and excitons, it is found that the efficiency of the exciton-formation process and the temporal evolution of the resulting population are sensitive to the excitation energy. We discuss the effects on luminescence experiments

Mechanical Thrombectomy Versus Best Medical Treatment in the Late Time Window in Non-DEFUSE-Non-DAWN Patients: A Multicenter Cohort Study

Background: We assessed the efficacy and safety of mechanical thrombectomy (MT) in adult stroke patients with anterior circulation large vessel occlusion presenting in the late time window not fulfilling the DEFUSE-3 (Thrombectomy for Stroke at 6 to 16 Hours With Selection by Perfusion Imaging trial) and DAWN (Thrombectomy 6 to 24 Hours After Stroke With a Mismatch Between Deficit and Infarct trial) inclusion criteria. Methods: Cohort study of adults with anterior circulation large vessel occlusion admitted between 6 and 24 hours after last-seen-well at 5 participating Swiss stroke centers between 2014 and 2021. Mismatch was assessed by computer tomography or magnetic resonance imaging perfusion with automated software (RAPID or OLEA). We excluded patients meeting DEFUSE-3 and DAWN inclusion criteria and compared those who underwent MT with those receiving best medical treatment alone by inverse probability of treatment weighting using the propensity score. The primary efficacy end point was a favorable functional outcome at 90 days, defined as a modified Rankin Scale score shift toward lower categories. The primary safety end point was symptomatic intracranial hemorrhage within 7 days of stroke onset; the secondary was all-cause mortality within 90 days. Results: Among 278 patients with anterior circulation large vessel occlusion presenting in the late time window, 190 (68%) did not meet the DEFUSE-3 and DAWN inclusion criteria and thus were included in the analyses. Of those, 102 (54%) received MT. In the inverse probability of treatment weighting analysis, patients in the MT group had higher odds of favorable outcomes compared with the best medical treatment alone group (modified Rankin Scale shift: acOR, 1.46 [1.02–2.10]; P=0.04) and lower odds of all-cause mortality within 90 days (aOR, 0.59 [0.37–0.93]; P=0.02). There were no significant differences in symptomatic intracranial hemorrhage (MT versus best medical treatment alone: 5% versus 2%, P=0.63). Conclusions: Two out of 3 patients with anterior circulation large vessel occlusion presenting in the late time window did not meet the DEFUSE-3 and DAWN inclusion criteria. In these patients, MT was associated with higher odds of favorable functional outcomes without increased rates of symptomatic intracranial hemorrhage. These findings support the enrollment of patients into ongoing randomized trials on MT in the late window with more permissive inclusion criteria

Mechanical Thrombectomy For Large Vessel Occlusion Between 6 And 24 Hours: Outcome Comparison Of Defuse-3/Dawn Eligible Versus Non-Eligible Patients

The DEFUSE-3 and DAWN trials showed that mechanical thrombectomy (MT) improves the outcome of selected patients with large vessel occlusions in the anterior circulation (LVO) up to 24 hours of stroke onset. However, it is unknown whether only those patients fulfilling the trial inclusion criteria benefit, or whether benefit is seen in a broader range of patients presenting between 6 and 24 hours.; We determined whether fulfilling the DEFUSE-3 and DAWN selection criteria affects outcomes in MT patients in clinical practice.; We reviewed adult patients with LVO treated with MT between 6 and 24 hours after stroke onset at five Swiss stroke centers between 2014 and 2021. We compared two groups: (1) patients who satisfied neither DEFUSE-3 nor DAWN criteria (NDND); and (2) those who satisfied DEFUSE-3 or DAWN criteria (DOD). We used logistic regression to examine the impact of trial eligibility on two safety outcomes (symptomatic intracranial hemorrhage [sICH] and all-cause mortality at three months) and two efficacy outcomes (modified Rankin Score [mRS] shift toward lower categories and mRS of 0-2 at three months).; Of 174 patients who received MT, 102 (59%) belonged to the NDND group. Rates of sICH were similar between the NDND group and the DOD group (3% vs. 4%, p=1.00). Multivariable regression revealed no differences in 3-month all-cause mortality (aOR 2.07, 95%CI 0.64-6.84, p=0.23) or functional outcomes (mRS shift: acOR 0.81, 95%CI 0.37-1.79, p=0.60; mRS 0-2: aOR 0.91, 95%CI 0.31-2.57, p=0.85).; Among adult patients with LVO treated with MT between 6 and 24 hours, safety and efficacy outcomes were similar between DEFUSE-3/DAWN eligible vs. ineligible patients. Our data provide a compelling rationale for randomized trials with broader inclusion criteria for MT