Enhanced Efficiency at Maximum Power in a Fock-Darwin Model Quantum Dot Engine.

We study the performance of an endoreversible magnetic Otto cycle with a working substance composed of a single quantum dot described using the well-known Fock-Darwin model. We find that tuning the intensity of the parabolic trap (geometrical confinement) impacts the proposed cycle's performance, quantified by the power, work, efficiency, and parameter region where the cycle operates as an engine. We demonstrate that a parameter region exists where the efficiency at maximum output power exceeds the Curzon-Ahlborn efficiency, the efficiency at maximum power achieved by a classical working substance.

Otto Engine for the q-State Clock Model.

This present work explores the performance of a thermal-magnetic engine of Otto type, considering as a working substance an effective interacting spin model corresponding to the q- state clock model. We obtain all the thermodynamic quantities for the q = 2, 4, 6, and 8 cases in a small lattice size (3×3 with free boundary conditions) by using the exact partition function calculated from the energies of all the accessible microstates of the system. The extension to bigger lattices was performed using the mean-field approximation. Our results indicate that the total work extraction of the cycle is highest for the q=4 case, while the performance for the Ising model (q=2) is the lowest of all cases studied. These results are strongly linked with the phase diagram of the working substance and the location of the cycle in the different magnetic phases present, where we find that the transition from a ferromagnetic to a paramagnetic phase extracts more work than one of the Berezinskii-Kosterlitz-Thouless to paramagnetic type. Additionally, as the size of the lattice increases, the extraction work is lower than smaller lattices for all values of q presented in this study.

Short-Range Berezinskii-Kosterlitz-Thouless Phase Characterization for the q-State Clock Model.

Beyond the usual ferromagnetic and paramagnetic phases present in spin systems, the usual q-state clock model presents an intermediate vortex state when the number of possible orientations q for the system is greater than or equal to 5. Such vortex states give rise to the Berezinskii-Kosterlitz-Thouless (BKT) phase present up to the XY model in the limit q→∞. Based on information theory, we present here an analysis of the classical order parameters plus new short-range parameters defined here. Thus, we show that even using the first nearest neighbors spin-spin correlations only, it is possible to distinguish the two transitions presented by this system for q greater than or equal to 5. Moreover, the appearance at relatively low temperature and disappearance of the BKT phase at a rather fix higher temperature is univocally determined by the short-range interactions recognized by the information content of classical and new parameters.

Otto Engine: Classical and Quantum Approach.

In this paper, we analyze the total work extracted and the efficiency of the magnetic Otto cycle in its classic and quantum versions. As a general result, we found that the work and efficiency of the classical engine is always greater than or equal to its quantum counterpart, independent of the working substance. In the classical case, this is due to the fact that the working substance is always in thermodynamic equilibrium at each point of the cycle, maximizing the energy extracted in the adiabatic paths. We apply this analysis to the case of a two-level system, finding that the work and efficiency in both the Otto's quantum and classical cycles are identical, regardless of the working substance, and we obtain similar results for a multilevel system where a linear relationship between the spectrum of energies of the working substance and the external magnetic field is fulfilled. Finally, we show an example of a three-level system in which we compare two zones in the entropy diagram as a function of temperature and magnetic field to find which is the most efficient region when performing a thermodynamic cycle. This work provides a practical way to look for temperature and magnetic field zones in the entropy diagram that can maximize the power extracted from an Otto magnetic engine.

Magnetic Otto Engine for an Electron in a Quantum Dot: Classical and Quantum Approach.

We studied the performance of classical and quantum magnetic Otto cycle with a working substance composed of a single quantum dot using the Fock-Darwin model with the inclusion of the Zeeman interaction. Modulating an external/perpendicular magnetic field, in the classical approach, we found an oscillating behavior in the total work extracted that was not present in the quantum formulation.We found that, in the classical approach, the engine yielded a greater performance in terms of total work extracted and efficiency than when compared with the quantum approach. This is because, in the classical case, the working substance can be in thermal equilibrium at each point of the cycle, which maximizes the energy extracted in the adiabatic strokes.

Magnetocaloric Effect in Non-Interactive Electron Systems: "The Landau Problem" and Its Extension to Quantum Dots.

In this work, we report the magnetocaloric effect (MCE) in two systems of non-interactive particles: the first corresponds to the Landau problem case and the second the case of an electron in a quantum dot subjected to a parabolic confinement potential. In the first scenario, we realize that the effect is totally different from what happens when the degeneracy of a single electron confined in a magnetic field is not taken into account. In particular, when the degeneracy of the system is negligible, the magnetocaloric effect cools the system, while in the other case, when the degeneracy is strong, the system heats up. For the second case, we study the competition between the characteristic frequency of the potential trap and the cyclotron frequency to find the optimal region that maximizes the ΔT of the magnetocaloric effect, and due to the strong degeneracy of this problem, the results are in coherence with those obtained for the Landau problem. Finally, we consider the case of a transition from a normal MCE to an inverse one and back to normal as a function of temperature. This is due to the competition between the diamagnetic and paramagnetic response when the electron spin in the formulation is included.

Magnetocaloric Effect in an Antidot: The Effect of the Aharonov-Bohm Flux and Antidot Radius.

In this work, we report the magnetocaloric effect (MCE) for an electron interacting with an antidot, under the effect of an Aharonov-Bohm flux (AB-flux) subjected to a parabolic confinement potential. We use the Bogachek and Landman model, which additionally allows the study of quantum dots with Fock-Darwin energy levels for vanishing antidot radius and AB-flux. We find that AB-flux strongly controls the oscillatory behaviour of the MCE, thus acting as a control parameter for the cooling or heating of the magnetocaloric effect. We propose a way to detect AB-flux by measuring temperature differences.

Quantum Mechanical Engine for the Quantum Rabi Model.

We consider a purely mechanical quantum cycle comprised of adiabatic and isoenergetic processes. In the latter, the system interacts with an energy bath keeping constant the expectation value of the Hamiltonian. In this work, we study the performance of the quantum cycle for a system described by the quantum Rabi model for the case of controlling the coupling strength parameter, the resonator frequency, and the two-level system frequency. For the cases of controlling either the coupling strength parameter or the resonator frequency, we find that it is possible to closely approach to maximal unit efficiency when the parameter is sufficiently increased in the first adiabatic stage. In addition, for the first two cases the maximal work extracted is obtained at parameter values corresponding to high efficiency, which constitutes an improvement over current proposals of this cycle.

Entropy and Mutability for the q-State Clock Model in Small Systems.

In this paper, we revisit the q-state clock model for small systems. We present results for the thermodynamics of the q-state clock model for values from q = 2 to q = 20 for small square lattices of L × L , with L ranging from L = 3 to L = 64 with free-boundary conditions. Energy, specific heat, entropy, and magnetization were measured. We found that the Berezinskii-Kosterlitz-Thouless (BKT)-like transition appears for q > 5, regardless of lattice size, while this transition at q = 5 is lost for L < 10; for q ≤ 4, the BKT transition is never present. We present the phase diagram in terms of q that shows the transition from the ferromagnetic (FM) to the paramagnetic (PM) phases at the critical temperature T 1 for small systems, and the transition changes such that it is from the FM to the BKT phase for larger systems, while a second phase transition between the BKT and the PM phases occurs at T 2. We also show that the magnetic phases are well characterized by the two-dimensional (2D) distribution of the magnetization values. We made use of this opportunity to carry out an information theory analysis of the time series obtained from Monte Carlo simulations. In particular, we calculated the phenomenological mutability and diversity functions. Diversity characterizes the phase transitions, but the phases are less detectable as q increases. Free boundary conditions were used to better mimic the reality of small systems (far from any thermodynamic limit). The role of size is discussed.

Patterning of sub-50 nm perpendicular CoFeB/MgO-based magnetic tunnel junctions.

Perpendicular magnetic tunnel junctions (p-MTJs) were patterned into nanopillars using electron-beam lithography to study their scaling and switching behaviour. Magnetoresistance measurements of annealed and unannealed p-MTJ films using scanning probe microscopy showed good agreement with Monte Carlo modeling. p-MTJ pillars demonstrated clear parallel magnetic states, both 'up' or both 'down' following AC-demagnetization. Significant variability in the resistance of p-MTJ pillars was observed and attributed to edge features generated during patterning or local inhomogeneity in the MgO layer.

Inferior Vena Cava Thrombosis Related to Hypothermia Catheter: Report of 20 Consecutive Cases.

BACKGROUND: Temperature management using endovascular catheters is an established therapy in neurointensive care. Nonetheless, several case series have reported a high rate of thrombosis related to the use of endovascular hypothermia catheters. METHODS: As a result of a pulmonary embolism that developed in a patient after removing an inferior vena cava hypothermia catheter, we designed a clinical protocol for managing and removing these devices. First, an invasive cavography was performed before the removal of the catheter. If there was a thrombus, a cava vein filter was inserted through jugular access. After that, the catheter was removed. RESULTS: The venography found inferior vena cava thrombi in 18 of 20 consecutive patients. A concomitant ultrasonography study showed vena cava thrombosis in only three patients. A vena cava filter was inserted in all patients where thrombi were found, without any significant complication. Anticoagulation was started in all patients. No symptomatic pulmonary embolism was diagnosed until the time of discharge. CONCLUSIONS: The frequency of thrombosis related to temperature management catheters is extremely high (90 %). Furthermore, ultrasonography has a very low sensibility to detect cava vein thrombosis (16.7 %). The real meaning of our findings is unknown, but other temperature control systems could be a safer option. More studies are needed to confirm our findings.

Interventional solutions for post-surgical problems: a lymphatic leaks review.

The lymphatic circulation plays a crucial role in maintaining fluid balance and supporting immune responses by returning serum proteins and lipids to the systemic circulation. Lymphatic leaks, though rare, pose significant challenges post-radical neck surgery, oesophagectomy, and thoracic or retroperitoneal oncological resections, leading to heightened morbidity and mortality. Managing lymphatic leaks necessitates consideration of aetiology, severity, and volume of leakage. Traditionally, treatment involved conservative measures such as dietary restrictions, drainage, and medical management, with surgical intervention reserved for severe cases, albeit with variable outcomes and extended recovery periods. Lymphography, introduced in the 1950s, initially served as a diagnostic tool for lymphoedema, lymphoma, tumour staging, and monitoring chemotherapy response. However, its widespread adoption was impeded by alternative techniques like Computed Tomography, learning curves, and its associated complications. Contemporary lymphatic interventions have evolved, favouring nodal lymphangiography over pedal lymphangiography for its technical simplicity and reduced complexity. Effective management of chylous leaks mandates a multimodal approach encompassing clinical evaluation and imaging techniques. In cases where conservative management proves ineffective, embolization through conventional lymphangiography by bipedal dissection or intranodal injection emerges as a viable option. This review underscores the importance of a comprehensive approach to diagnosing and treating lymphatic leaks, highlighting advancements in imaging and therapeutic interventions that enhance patient outcomes.

[Association of carotid intima-media thickness with traditional cardiovascular risk and metabolic factors]. / Grosor íntima media carotídeo y asociación con factores de riesgo cardiovascular tradicionales y metabólicos.

BACKGROUND: Carotid intima-media thickness (IMT) is a surrogate marker of subclinical atherosclerosis and is associated with cardiovascular risk factors (CVRF) AIM: To analyze the association of CVRF and metabolic factors (MF) with IMT, and if the clustering of these factors modify IMT. MATERIAL AND METHODS: Cross sectional study in 187 participants aged 46±10 years (53% male) without CV disease. Weight, height, waist circumference (WC), blood pressure, fasting plasma glucose and lipid profile were measured. Abdominal obesity (AOb) was defined by ATP III criteria. Mean carotid IMT was measured at the far wall of the common carotid artery. The cutoff point for an abnormally high IMT was set at the 75th IMT percentile of the sample. RESULTS: The 75th IMT percentile of the sample was 0.67 mm. In a multivariate analysis four factors were significantly related with a high IMT: age (odds ratio (OR): 5.3, confidence intervals (CI): 2.2-12.9), dyslipidemia (OR: 6.4 CI: 2.3-17.9), systolic blood pressure (OR: 2.9, CI: 1.2-7.1) and AOb (OR: 2.9 (IC: 1.1-7.2). The presence of Oto 4 of these factors was associated with an IMT increment from 0.54 to 0.71 mm (p < 0,001). CONCLUSIONS: In this sample dyslipidemia, systolic blood pressure and abdominal obesity were the main predictors of a high IMT.

Caloric Effect Due to the Aharonov-Bohm Flux in an Antidot.

In this work, we report the caloric effect for an electronic system of the antidot type, modeled by combining a repulsive and attractive potential (parabolic confinement). In this system, we consider the action of a perpendicular external magnetic field and the possibility of having an Aharonov-Bohm flux (AB-flux) generated by a current passing through a solenoid placed inside the forbidden zone for the electron. The energy levels are obtained analytically, and the model is known as the Bogachek and Landman model. We propose to control the caloric response of the system by varying only the AB-flux, finding that, in the absence of an external magnetic field, the maximization of the effect always occurs at the same AB-flux intensity, independently of the temperature, while fixing the external magnetic field at a non-zero value breaks this symmetry and changes the point where the caloric phenomenon is maximized and is different depending on the temperature to which the process is carried. Our calculations indicate that using an effective electron mass of GaAs heterostructures and a trap intensity of the order of 2.896 meV, the modification of the AB-flux achieves a variation in temperature of the order of 1 K. Our analysis suggests that increasing the parabolic confinement twofold increases the effect threefold, while increasing the antidot size generates the reverse effect, i.e., a strong decrease in the caloric phenomenon under study. Due to the great diversity in technological applications that have antidots in electronics, the possibility of controlling their thermal response simply by varying the intensity of the internal current inside the solenoid (i.e., the intensity of AB-flux) can be a platform of interest for experimental studies.

Multilayer Graphene as an Endoreversible Otto Engine.

We examine the performance of a finite-time, endoreversible Otto heat engine with a working medium of monolayer or multilayered graphene subjected to an external magnetic field. As the energy spectrum of multilayer graphene under an external magnetic field depends strongly on the number of layers, so too does its thermodynamic behavior. We show that this leads to a simple relationship between the engine efficiency and the number of layers of graphene in the working medium. Furthermore, we find that the efficiency at maximum power for bilayer and trilayer working mediums can exceed that of a classical endoreversible Otto cycle. Conversely, a working medium of monolayer graphene displays identical efficiency at maximum power to a classical working medium. These results demonstrate that layered graphene can be a useful material for the construction of efficient thermal machines for diverse quantum device applications.

Intranodal Ultrasound-Guided Percutaneous Methylene Blue Injection for the Identification of Leakage Point during Laparoscopic Repair of Refractory Chylous Ascites after Laparoscopic Lymphadenectomy for Kidney Cancer.

Chylous ascites is an uncommon complication after surgery that can result in malnutrition and immunodeficiency. Therefore, surgical interventions are reserved for refractory patients, and the primary success factor for these interventions is locating the point of leakage, which is often tricky. We describe a case of a 56-year-old male with chylous ascites after laparoscopic radical nephrectomy and lumbo-aortic lymphadenectomy for kidney cancer. The patient was initially managed with dietary modifications and drainage placement. Afterward, lymphography with Lipiodol, percutaneous embolization of the leakage point, and total parenteral nutrition were established. Finally, the patient underwent laparoscopic repair after identifying the leakage point by injecting methylene blue through an inguinal node. Complete resolution was achieved, and no complications related to the procedure were recorded. Intranodal methylene blue injection can be an invaluable tool to identify the point of leakage in selected patients to improve the outcomes of surgical repair of refractory chylous ascites.

High Flow Nasal Cannula Oxygenation Successfully Used as Bridge Therapy for Systemic Thrombolysis in COVID-19 Associated Intermediate-high Risk Pulmonary Embolism.

The risk of venous thromboembolism (VTE) in COVID-19 patients is a growing problem. Thromboembolic complications are associated with the infection by SARSCoV-2, with an estimated incidence up to 25%-30% of VTE in patients with severe COVID-19 pneumonia. Here in, we present a case of a patient with severe pneumonia due to COVID-19 who is admitted with mild pneumothorax secondary to COVID-19 and high-intermediate-risk pulmonary embolism (PE), who underwent successfully a highflow nasal cannula (HFNC) oxygenation bridge with subsequent successful half-doses of systemic thrombolysis with intravenous alteplase. Prospective studies are warranted in this subset of patients with intermediate-high and high-risk PE, to further explore HFNC oxygenation with or without diverse reperfusion strategies, with the aim to identify the best individualized therapeutic approach in each patient with significant COVID-19 associated VTE and optimize outcomes.

Continuous prolonged prone positioning in COVID-19-related ARDS: a multicenter cohort study from Chile.

BACKGROUND: Prone positioning is currently applied in time-limited daily sessions up to 24 h which determines that most patients require several sessions. Although longer prone sessions have been reported, there is scarce evidence about the feasibility and safety of such approach. We analyzed feasibility and safety of a continuous prolonged prone positioning strategy implemented nationwide, in a large cohort of COVID-19 patients in Chile. METHODS: Retrospective cohort study of mechanically ventilated COVID-19 patients with moderate-to-severe acute respiratory distress syndrome (ARDS), conducted in 15 Intensive Care Units, which adhered to a national protocol of continuous prone sessions ≥ 48 h and until PaO2:FiO2 increased above 200 mm Hg. The number and extension of prone sessions were registered, along with relevant physiologic data and adverse events related to prone positioning. The cohort was stratified according to the first prone session duration: Group A, 2-3 days; Group B, 4-5 days; and Group C, > 5 days. Multivariable regression analyses were performed to assess whether the duration of prone sessions could impact safety. RESULTS: We included 417 patients who required a first prone session of 4 (3-5) days, of whom 318 (76.3%) received only one session. During the first prone session the main adverse event was grade 1-2 pressure sores in 97 (23.9%) patients; severe adverse events were infrequent with 17 non-scheduled extubations (4.2%). 90-day mortality was 36.2%. Ninety-eight patients (24%) were classified as group C; they exhibited a more severe ARDS at baseline, as reflected by lower PaO2:FiO2 ratio and higher ventilatory ratio, and had a higher rate of pressure sores (44%) and higher 90-day mortality (48%). However, after adjustment for severity and several relevant confounders, prone session duration was not associated with mortality or pressure sores. CONCLUSIONS: Nationwide implementation of a continuous prolonged prone positioning strategy for COVID-19 ARDS patients was feasible. Minor pressure sores were frequent but within the ranges previously described, while severe adverse events were infrequent. The duration of prone session did not have an adverse effect on safety.

Gate-tunable charge carrier electrocaloric effect in trilayer graphene.

The electrocaloric (EC) effect is the change in temperature and entropy of a material driven by the application of an electric field. Our tight-binding calculations linked to Fermi statistics, show that the EC effect can be produced in trilayer graphene (TLG) structures connected to a heat source, triggered by changes in the electronic density of states (DOS) at the Fermi level when external gate fields are applied on the outer graphene layers. We demonstrate that entropy changes are sensitive to the stacking arrangement in TLG systems. The AAA-stacked TLG presents an inverse EC response (cooling) regardless of the temperature value and gate field potential strength, whereas the EC effect in ABC-stacked TLG remains direct (heating) above room temperature. We reveal otherwise the TLG with Bernal-ABA stacking generates both the direct and inverse EC response within the same sample, associated with gate-dependent electronic transitions of thermally excited charge carriers from the valence band to the conduction band in the band structure. The novel charge carrier electrocaloric effect we propose in quantum layered systems may bring a wide variety of prototype van der Waals materials that could be used as versatile platforms to controlling the thermal response in nanodevices.