Fiber-orientation independent component of R2* obtained from single-orientation MRI measurements in simulations and a post-mortem human optic chiasm

The effective transverse relaxation rate (R2*) is sensitive to the microstructure of the human brain like the g-ratio which characterises the relative myelination of axons. However, the fibre-orientation dependence of R2* degrades its reproducibility and any microstructural derivative measure. To estimate its orientation-independent part (R2,iso*) from single multi-echo gradient-recalled-echo (meGRE) measurements at arbitrary orientations, a second-order polynomial in time model (hereafter M2) can be used. Its linear time-dependent parameter, β1, can be biophysically related to R2,iso* when neglecting the myelin water (MW) signal in the hollow cylinder fibre model (HCFM). Here, we examined the performance of M2 using experimental and simulated data with variable g-ratio and fibre dispersion. We found that the fitted β1 can estimate R2,iso* using meGRE with long maximum-echo time (TEmax ≈ 54 ms), but not accurately captures its microscopic dependence on the g-ratio (error 84%). We proposed a new heuristic expression for β1 that reduced the error to 12% for ex vivo compartmental R2 values. Using the new expression, we could estimate an MW fraction of 0.14 for fibres with negligible dispersion in a fixed human optic chiasm for the ex vivo compartmental R2 values but not for the in vivo values. M2 and the HCFM-based simulations failed to explain the measured R2*-orientation-dependence around the magic angle for a typical in vivo meGRE protocol (with TEmax ≈ 18 ms). In conclusion, further validation and the development of movement-robust in vivo meGRE protocols with TEmax ≈ 54 ms are required before M2 can be used to estimate R2,iso* in subjects

Fiber-orientation independent component of R2* obtained from single-orientation MRI measurements in simulations and a post-mortem human optic chiasm

The effective transverse relaxation rate (R2*) is sensitive to the microstructure of the human brain like the g-ratio which characterises the relative myelination of axons. However, the fibre-orientation dependence of R2* degrades its reproducibility and any microstructural derivative measure. To estimate its orientation-independent part (R2,iso*) from single multi-echo gradient-recalled-echo (meGRE) measurements at arbitrary orientations, a second-order polynomial in time model (hereafter M2) can be used. Its linear time-dependent parameter, β1, can be biophysically related to R2,iso* when neglecting the myelin water (MW) signal in the hollow cylinder fibre model (HCFM). Here, we examined the performance of M2 using experimental and simulated data with variable g-ratio and fibre dispersion. We found that the fitted β1 can estimate R2,iso* using meGRE with long maximum-echo time (TEmax ≈ 54 ms), but not accurately captures its microscopic dependence on the g-ratio (error 84%). We proposed a new heuristic expression for β1 that reduced the error to 12% for ex vivo compartmental R2 values. Using the new expression, we could estimate an MW fraction of 0.14 for fibres with negligible dispersion in a fixed human optic chiasm for the ex vivo compartmental R2 values but not for the in vivo values. M2 and the HCFM-based simulations failed to explain the measured R2*-orientation-dependence around the magic angle for a typical in vivo meGRE protocol (with TEmax ≈ 18 ms). In conclusion, further validation and the development of movement-robust in vivo meGRE protocols with TEmax ≈ 54 ms are required before M2 can be used to estimate R2,iso* in subjects

Time from diagnosis to treatment has no impact on survival in newly diagnosed acute myeloid leukemia treated with venetoclax-based regimens

In newly diagnosed acute myeloid leukemia, immediate initiation of treatment is standard of care. However, deferral of antileukemic therapy may be indicated to assess comorbidities or pre-therapeutic risk factors. We explored the impact of time from diagnosis to treatment on outcomes in newly diagnosed acute myeloid leukemia undergoing venetoclax-based therapy in two distinct cohorts. By querying the Study Alliance Leukemia database and the global health network TriNetX, we identified 138 and 717 patients respectively with an average age of 76 and 72 years who received venetoclax-based firstline therapy. When comparing patients who started treatment earlier or later than 10 days after initial diagnosis, no significant difference in median overall survival was observed - neither in the SAL cohort (7.7 vs. 9.6 months, p=.42) nor in the TriNetX cohort (7.5 vs. 7.2 months, p=.41). Similarly, severe infections, bleeding, and thromboembolic events were equally observed between early and later treatments, both in the overall patient groups and specific subgroups (age ≥75 years or leukocytes ≥20x109/L). This retrospective analysis indicates that delaying the start of venetoclax-based therapy in newly diagnosed acute myeloid leukemia might be a safe option for selected patients, provided that close clinical monitoring is performed

Herstellung und Eigenschaften hydridbasierter Verbundwerkstoffe mit hoher Energie- und Leistungsdichte für die Wasserstoffspeicherung

In dieser Arbeit werden kompaktierte Verbundwerkstoffe aus verschiedenen Speichermaterialien mit expandiertem Naturgraphit (ENG) in Hinblick auf die Anwendung als dynamische Wasserstofffeststoffspeichermaterialien untersucht. Pulverförmige hydridbildende Ausgangsmaterialien wurden mit bis zu 25 Masse-% ENG vermischt und bei Pressdrücken bis 600 MPa kompaktiert. Um einen weiten Anwendungsbereich abzudecken wurden ein Niedrigtemperaturmaterial (Ti-Mn-basierte Legierung; 0°C bis 100°C), zwei Mitteltemperaturmaterialien (Amid- und Alanatsystem; 100°C bis 200°C) und ein Hochtemperaturmaterial (Magnesium-Nickel-Legierung; 250°C bis 400°C) basierend auf einer umfangreichen Literaturrecherche gewählt. Die Verbundwerkstoffe weisen eine erhöhte radiale Wärmeleitfähigkeit auf und zeichnen sich im Vergleich zu herkömmlich verwendeten Pulverschüttungen durch höhere volumetrische Wasserstoffspeicherdichten aus. Im Fokus der Untersuchungen stehen vor allem die im Hinblick auf Anwendungstauglichkeit wesentlichen Eigenschaften der Verbundwerkstoffe. So wurde z.B. der Wasserstoffdruck während der Dehydrierung variiert, um sicher zu stellen, Verbraucher mit üblichen Überdrücken versorgen zu können. Darüber hinaus wurde die Stabilität, Gaspermeabilität, Wärmeleitfähigkeit und Porosität der Presslinge im Verlauf zyklischer Hydrierung evaluiert und diskutiert. Insgesamt zeichnet sich ein hohes Potenzial ab, derartige Presslinge als Wasserstoffspeichermaterial für verschiedene Anwendungen entsprechend der jeweiligen Arbeitstemperaturen und weiteren Randbedingungen (z.B. Systemmasse, Tankvolumen etc.) zu verwenden. Diesbezüglich konnte mittels eines Tankdemonstrators basierend auf dem Ti-Mn-System ein Wasserstofffahrzeug erfolgreich betrieben und somit auch die Praxistauglichkeit der Hydrid-Graphit-Verbundmaterialien gezeigt werden.Compacted composites of solid-state hydrogen storage materials and expanded natural graphite (ENG) are investigated in view of their potential for hydrogen storage applications. Powdery hydride-forming materials were blended with up to 25 weight-% ENG and compacted with up to 600 MPa compaction pressure. In order to cover a wide range of possible applications one low-temperature material (Ti-Mn-based alloy; 0°C to 100°C), two mid-temperature materials (amide and alante system; 100°C to 200°C) and one high-temperature material (magnesium-nickel alloy; 250°C to 400°C) were chosen based on a thorough literature review. The composites result in an increased radial thermal conductivity and are superior in their volumetric hydrogen storage density compared to commonly used loose powder beds. The research is focused on the applicability of suchlike prepared composites. In this regard, the dehydrogenation back-pressures were varied to ensure a sufficient supply pressure of common consumer loads. Furthermore, the stability, gas permeability, thermal conductivity and porosity throughout cyclic hydrogenation were evaluated and discussed. Overall, a high potential to use suchlike composite materials for hydrogen storage applications regarding the specific working conditions (temperature, system mass, available volume etc.) is found. In this regard, a demonstrator tank equipped with Ti-Mn-based system was successfully supplying a hydrogen driven vehicle, which proves the feasibility of these hydride-graphite composite materials

Speicherelement für Gase

Die Erfindung betrifft ein Speicherelement für Gase, bei dem in einem starren innen hohlen Gehäuse, das mindestens eine Zu-, eine Abführung oder eine Zu- und Abführung für ein Gas aufweist, ein Sorptionsmittel für die Speicherung eines jeweiligen Gases in mindestens einem Bereich aufgenommen ist. Im Gehäuse ist mindestens ein weiterer Bereich vorhanden, in dem ein elastisch verformbarer Körper oder ein elastisch verformbares Material aufgenommen und kein Sorptionsmittel vorhanden ist. Der Körper oder das Material ist soweit elastisch verformbar und/oder sein Volumen so dimensioniert, dass eine Volumenausdehnung des Sorptionsmittels bei der Sorption des jeweiligen Gases kompensierbar ist

Long-term cycle stability of metal hydride-graphite composites

Recently, metal hydride composites (MHC) have been proposed which consist of a hydride forming metal alloy and a highly heat conduction secondary phase such as expanded natural graphite (ENG) in order to improve the thermal conductivity of metal hydride powder beds. However, only little data is available in the literature on the effects of extensive cycling on technically relevant properties of MHC. In this paper, hydrogenation characteristics, thermal conductivity and geometrical stability of Hydralloy® C5-based MHC were thoroughly investigated over 1000 cycles. The obtained results suggest that the MHC under study did not significantly alter their hydrogen uptake characteristics throughout cycling, despite the fact that their thermal conductivity decreased during the first 250 cycles but remained constant thereafter. Although the cylindrical MHC maintained their geometrical stability, radial cracks were detected after cycling. Based on these results, MHC are suitable for high-dynamic applications such as hydrogen storage or thermochemical devices

Standardized hydrogen storage module with high utilization factor based on metal hydride-graphite composites

In view of hydrogen based backup power systems or small-scale power2gas units, hydrogen storages based on metal hydrides offer a safe and reliable solution. By using Hydralloy C5 as suitable hydride forming alloy, the present tank design guarantees very simple operating conditions: pressures between 4 bar and 30 bar, temperatures between 15 C and 40 C and minimal efforts for thermal management in combination with fast and constant charging and discharging capabilities. The modular tank consists of 4 layers with 5 reactor tubes each that are filled with metal hydride-graphite composites of a diameter of 21 mm. Experiments show that each layer of this tank is able to desorb the desired amount of hydrogen for a fuel cell operation at electrical power of 160 Wel for 100 min reaching a utilization factor of 93% of the stored hydrogen at RC. Furthermore, the experimental results of modularity, increasing loads and the electric air ventilation are presented

Deformation at ambient and high temperature of in situ Laves phases-ferrite composites

The mechanical behavior of a Fe80Zr10Cr10 alloy has been studied at ambient and high temperature. This Fe80Zr10Cr10 alloy, whoose microstructure is formed by alternate lamellae of Laves phase and ferrite, constitutes a very simple example of an in situ CMA phase composite. The role of the Laves phase type was investigated in a previous study while the present work focuses on the influence of the microstructure length scale owing to a series of alloys cast at different cooling rates that display microstructures with Laves phase lamellae width ranging from ∼50 nm to ∼150 nm. Room temperature compression tests have revealed a very high strength (up to 2 GPa) combined with a very high ductility (up to 35%). Both strength and ductility increase with reduction of the lamella width. High temperature compression tests have shown that a high strength (900 MPa) is maintained up to 873 K. Microstructural study of the deformed samples suggests that the confinement of dislocations in the ferrite lamellae is responsible for strengthening at both ambient and high temperature. The microstructure scale in addition to CMA phase structural features stands then as a key parameter for optimization of mechanical properties of CMA in situ composites