Elektron transzport molekuláris nanostruktúrákban = Electron transport in molecular nanostructures

Az OTKA K76010 kutatói pályázat keretében nanokontaktusok viselkedését vizsgáltuk, melyekben az áram egyetlen atomon vagy egyetlen molekulán keresztül folyik. A kutatás keretében kifejlesztettünk egy molekulák kontrollált adagolására alkalmas mérőrendszert, mely egyedi molekulák kontaktálását teszi lehetővé folyékony hélium hőmérsékleten. Szupravezető subgap módszerrel karakterizáltunk különböző anyagból készült atomi méretű kontaktusokat és elméleti csoportokkal együttműködve részt vettünk egy vezetőképesség hisztogramok szimulálására alkalmas módszer fejlesztésében, melynek megbízhatóságát a subgap módszer segítségével egyedi vezetési csatornák szintjén ellenőriztük. Kifejlesztettünk egy új statisztikai módszert, melynek segítségével atomi és molekuláris kontaktusokban kialakuló konfigurációk közötti korrelációk vizsgálhatók. Ezen módszer segítségével számos atomi és molekuláris nanovezeték viselkedését sikerült a szokásos vezetőképesség hisztogram technikánál részletesebben feltérképezni. | Within the OTKA K76010 project nano-scale junctions were investigated, in which the current flows along single atoms or molecules. A novel measurement setup was developed which is capable of a controlled dosing of molecules to a liquid helium temperature break junction device so that single molecules can be contacted in a well controlled manner. With the help of superconducting subgap structure measurements various metal atomic sized contacts were characterized. In collaboration with theory groups a novel method was developed to simulate conductance histograms. With the help of subgap structure measurements the reliability of this method was tested on the level of individual channel transmission eigenvalues. Beside, we have introduced a novel statistical analysis method based on the two-dimensional cross-correlation histogram analysis of conductance traces. This method provides new information about the relation of different junction configurations that occur during the formation and evolution of metal and single-molecule junctions. The correlation method was successfully applied to study the behavior a several atomic and single-molecule structures beyond conductance histograms

Strong nonlocal tuning of the current-phase relation of a quantum dot based Andreev molecule

Multiple systems hosting Andreev molecular states have been proposed and studied, consisting of closely spaced Josephson junctions modeled as ballistic channels. We show that replacing the ballistic channels in the weak link of the Josephson junctions with quantum dots (QD), leads to a very exciting, rich phase diagram. It shows a strong nonlocal Josephson effect: as one junction is tuned the current-phase relation of the other junction is modified. This architecture hosts $0 - \pi$ transitions and shows a tunable anomalous phase-shift $\phi_0$ , nonlocally controlled in both cases, without relying on spin-orbit interaction or Zeeman fields. In addition significant superconducting diode effect can also be observed. The presented non-local current-phase relation can be used as a signature of the formation of an Andreev molecular state, as well as to introduce new ways to tune quantum architectures

Point contacts in encapsulated graphene

We present a novel method to establish inner point contacts on hexagonal boron nitride (hBN) encapsulated graphene heterostructures with dimensions as small as 100 nm by pre-patterning the top-hBN in a separate step prior to dry-stacking. 2 and 4-terminal field effect measurements between different lead combinations are in qualitative agreement with an electrostatic model assuming pointlike contacts. The measured contact resistances are 0.5-1.5 k$\Omega$ per contact, which is quite low for such small contacts. By applying a perpendicular magnetic fields, an insulating behaviour in the quantum Hall regime was observed, as expected for inner contacts. The fabricated contacts are compatible with high mobility graphene structures and open up the field for the realization of several electron optical proposals

Urban Bus Network Electrification

Electric busses are spreading in cities in hope of mitigating local air pollution. Currently, battery electric busses are more expensive and require novel operational methods to optimize their use (e.g., applying daytime charging, and operating trolleybuses). Despite these, the electrification of urban busses is usually ad-hoc, preliminary planning is superficial, and does not consider the relationships among bus lines. This chapter introduces a method regarding charging infrastructure planning, electric bus type selection, and cost estimation. Based on the characteristics of the vehicle, charging infrastructure, bus service (lines, timetable, etc.), and energy consumption, a line-group optimization is introduced, which is the main novelty. The method was applied in a case study considering static terminal and dynamic catenary charging. The results help operators to boost the electrification of the urban bus network

Preconditioning protects the heart in a prolonged uremic condition

Metabolic diseases such as hyperlipidemia and diabetes attenuate the cardioprotective effect of ischemic preconditioning. In the present study, we examined whether another metabolic disease, prolonged uremia, affects ischemia/reperfusion injury and cardioprotection by ischemic preconditioning. Uremia was induced by partial nephrectomy in male Wistar rats. The development of uremia was verified 29 wk after surgery. Transthoracic echocardiography was performed to monitor cardiac function. At week 30, hearts of nephrectomized and sham-operated rats were isolated and subjected to a 30-min coronary occlusion followed by 120 min reperfusion with or without preceding preconditioning induced by three intermittent cycles of brief ischemia and reperfusion. In nephrectomized rats, plasma uric acid, carbamide, and creatinine as well as urine protein levels were increased as compared with sham-operated controls. Systolic anterior and septal wall thicknesses were increased in nephrectomized rats, suggesting the development of a minimal cardiac hypertrophy. Ejection fraction was decreased and isovolumic relaxation time was shortened in nephrectomized rats demonstrating a mild systolic and diastolic dysfunction. Infarct size was not affected significantly by nephrectomy itself. Ischemic preconditioning significantly decreased infarct size from 24.8 ± 5.2% to 6.6 ± 1.3% in the sham-operated group and also in the uremic group from 35.4 ± 9.5% to 11.9 ± 3.1% of the area at risk. Plasma ANG II and nitrotyrosine were significantly increased in the uremic rats. We conclude that although prolonged experimental uremia leads to severe metabolic changes and the development of a mild myocardial dysfunction, the cardioprotective effect of ischemic preconditioning is still preserved

A szívizom sztressz-adaptációja: a peroxinitrit, a mátrix metalloproteinázok, és a hiperlipidémia szerepe = Stress adaptation of the myocardium: role of peroxynitrite, matrix metalloproteinases, and hyperlipidemia

A hiperlipidémia talaján kialakuló iszkémiás szívbetegség a leggyakoribb halálokok közé tartozik. A 4 éves project során a szívizom iszkémiának és az iszkémiás stressz adaptációs képességének (iszkémiás pre- és posztkondíció) celluláris mechanizmusait vizsgáltuk állatkísérletekben, különösképpen a peroxinitrit és celluláris targetjének, az MMP2-nek a szerepét. Új eredményeink közül néhányat emelünk ki. Kimutattuk, hogy hiperlipidemiában a szívben a peroxitrit képződés és ezáltal az MMP-2 aktivitása fokozódik, ami különösen hiperlipidmémiában jelentős, és ezt a folyamatot a prékondíció gátolja. DNA-chip vizsgálattal feltérképeztük hiperlipidémia hatására a génkifejeződés változásait a szívizomban. Kimutattuk, hogy az alacsony mértékű peroxinitrit képződés a stessz adaptáció kiváltásában igen fontos szerepet tölt be, hiszen olyan mechanizmusokat aktivál, melyek az iszkémiás stressz során túlzott mértékű peroxinitrit-MMP aktivitást csökkenti. Leírtuk, hogy nemspecifikus MMP gátlókkal az infarktus területe csökkenthető még hiperlipidémiás állatban is. Humán ApoB100 transzgenetikus eger modelleken megfigyeltük, hogy az oxidatív/nitrozatív stressz oka a hiperkoleszterinémia, és nem a hipertrigliceridémia. Kimutattuk továbbá, hogy a fiziológiás peroxinitrit szint, melyet a szívizom kapszaicin-érzékeny neuronjai szabályoznak, a normális szívizom relaxációt tartja fent. A project futamideje alatt az adott témában összesen 16 nemzetközi cikket (impakt faktor >70) közöltünk. | Ischemic heart disease developing due to hyperlipidemia is the number one killer in civilized societies. The present 4-year project was aiming at exploration of cellular mechanisms underlying stress adaptation of the myocardium, i.e. pre- and postconditioning, focusing on the role of peroxynitrite and its cellular target matrix metalloproteinase-2 (MMP2). Here we emphasize only some of the most important results of the project. We have shown that in hyperlipidemia, myocardial peroxynitrite formation and thereby MMP2 activity is increased, which is attenuated by preconditioning. We have mapped the changes in gene expression due to hyperlipidemia by the use of DNA-microarray assay. We have observed that moderate peroxynitrite formation is necessary to trigger the stress adaptation mechanisms, which in turn will decrease the pathological activation of the peroxynitrite-MMP2 signaling. We have shown that nonspecific MMP inhibitors are able to reduce infarct size even in the presence of hyperlipidemia. In human ApoB-100 transgene mice, we have observed that oxidative/nitrosative stress is due to hypercholesterolemia and not hypertriglyceridemia. Furthermore, we have shown that baseline physiological peroxynitrite formation, which is regulated by myocardial capsaicin-sensitive sensory nerves, plays an important role in the maintenance of normal relaxation of the myocardium. The present project yielded altogether 16 peer-reviewed papers (impact factor >70)