120 research outputs found
Water in acid boralites: Hydration effects on framework B sites
Properties and behavior of protonated boron-containing zeolites at different hydration degree have been investigated by means of periodic DFT approaches. Geometry optimization and room-temperature Car-Parrinello molecular dynamics results, in line with experimental findings, indicate that the BO3-bound silanolic acid site typical of dry boralites should convert to a solvated H3O+ hydrogen bonded to tetrahedral BO4 at moderate water content. By increasing the water loading, the tetrahedral structure of the B site is stabilized and the physicochemical properties of the water molecules solvating the acid proton gradually approach the liquid-phase ones. A relevant role of structural and vibrational properties of the zeolite framework in the water-induced trigonal-to-tetrahedral transition at the B site is highlighted by simulation results
Characterisation of flow dynamics within and around an isolated forest, through measurements and numerical simulations
The case study of ‘Bosco Fontana’, a densely-vegetated forest located in the north of Italy, is analysed both
experimentally and numerically to characterise the internal ventilation of a finite forest with a vertically
non-homogeneous canopy. Measurements allow for the evaluation of the turbulent exchange across the forest
canopy. The case study is then reproduced numerically via a two-dimensional RANS simulation, successfully
validated against experimental data. The analysis of the internal ventilation leads to the identification of
seven regions of motion along the predominate-wind direction, for whose definition a new in-canopy stability
parameter was introduced. In the vertical direction, the non-homogeneity of the canopy leads to the separation
of the canopy layer into an upper foliage layer and a lower bush layer, characterised respectively by an
increasing streamwise velocity and turbulence intensity, and a weak backflow. The conclusions report an
improved description of the dynamic layer and regions of motion presented in the literature
Urinary secretion and extracellular aggregation of mutant uromodulin isoforms
Uromodulin is exclusively expressed in the thick ascending limb and is the most abundant protein secreted in urine where it is found in high-molecular-weight polymers. Its biological functions are still elusive, but it is thought to play a protective role against urinary tract infection, calcium oxalate crystal formation, and regulation of water and salt balance in the thick ascending limb. Mutations in uromodulin are responsible for autosomal-dominant kidney diseases characterized by defective urine concentrating ability, hyperuricemia, gout, tubulointerstitial fibrosis, renal cysts, and chronic kidney disease. Previous in vitro studies found retention in the endoplasmic reticulum as a common feature of all uromodulin mutant isoforms. Both in vitro and in vivo we found that mutant isoforms partially escaped retention in the endoplasmic reticulum and reached the plasma membrane where they formed large extracellular aggregates that have a dominant-negative effect on coexpressed wild-type protein. Notably, mutant uromodulin excretion was detected in patients carrying uromodulin mutations. Thus, our results suggest that mutant uromodulin exerts a gain-of-function effect that can be exerted by both intra- and extracellular forms of the protein
Roughening of close-packed singular surfaces
An upper bound to the roughening temperature of a close-packed singular
surface, fcc Al (111), is obtained via free energy calculations based on
thermodynamic integration using the embedded-atom interaction model. Roughening
of Al (111) is predicted to occur at around 890 K, well below bulk melting (933
K), and it should therefore be observable, save for possible kinetic hindering.Comment: RevTeX 4 pages, embedded figure
Urinary secretion and extracellular aggregation of mutant uromodulin isoforms.
Uromodulin is exclusively expressed in the thick ascending limb and is the most abundant protein secreted in urine where it is found in high-molecular-weight polymers. Its biological functions are still elusive, but it is thought to play a protective role against urinary tract infection, calcium oxalate crystal formation, and regulation of water and salt balance in the thick ascending limb. Mutations in uromodulin are responsible for autosomal-dominant kidney diseases characterized by defective urine concentrating ability, hyperuricemia, gout, tubulointerstitial fibrosis, renal cysts, and chronic kidney disease. Previous in vitro studies found retention in the endoplasmic reticulum as a common feature of all uromodulin mutant isoforms. Both in vitro and in vivo we found that mutant isoforms partially escaped retention in the endoplasmic reticulum and reached the plasma membrane where they formed large extracellular aggregates that have a dominant-negative effect on coexpressed wild-type protein. Notably, mutant uromodulin excretion was detected in patients carrying uromodulin mutations. Thus, our results suggest that mutant uromodulin exerts a gain-of-function effect that can be exerted by both intra- and extracellular forms of the protein
The Northern Cross Fast Radio Burst project: III. The FRB-magnetar connection in a sample of nearby galaxies
Context. Fast radio bursts (FRBs) are millisecond radio transients observed at cosmological distances. The nature of their progenitors is still a matter of debate, although magnetars are invoked by most models. The proposed FRB-magnetar connection was strengthened by the discovery of an FRB-like event from the Galactic magnetar SGR J1935+2154.
Aims: In this work we aim to investigate how prevalent magnetars such as SGR J1935+2154 are within FRB progenitors.
Methods: To this end, we carried out an FRB search in a sample of seven nearby (< 12 Mpc) galaxies with the Northern Cross Radio Telescope for a total of 692 h.
Results: We detected one 1.8 ms burst in the direction of M 101 with a fluence of 58 ± 5 Jy ms. Its dispersion measure of 303 pc cm−3 places it most likely beyond M 101. Considering that no significant detection comes indisputably from the selected galaxies, we place a 38 yr−1 upper limit on the total burst rate (i.e. including the whole sample) at the 95% confidence level. This upper limit constrains the event rate per magnetar to λmag < 0.42 magnetar−1 yr−1 or, if combined with literature observations of a similar sample of nearby galaxies, it yields a joint constraint of λmag < 0.25 magnetar−1 yr−1. We also provide the first constraints on the expected rate of FRBs hypothetically originating from ultra-luminous X-ray (ULX) sources, since some of the galaxies observed during our observational campaign host confirmed ULXs. We obtain < 13 yr−1 per ULX for the total sample of galaxies observed.
Conclusions: Our results indicate that bursts with energies E > 1034 erg from magnetars such as SGR J1935+2154 appear more rarely compared to previous observations and further disfavour them as unique progenitors for the cosmological FRB population. This provides support to the idea that there is a greater contribution from a population of more exotic magnetars not born via core-collapsed supernovae
Generation of defects and disorder from deeply quenching a liquid to form a solid
We show how deeply quenching a liquid to temperatures where it is linearly
unstable and the crystal is the equilibrium phase often produces crystalline
structures with defects and disorder. As the solid phase advances into the
liquid phase, the modulations in the density distribution created behind the
advancing solidification front do not necessarily have a wavelength that is the
same as the equilibrium crystal lattice spacing. This is because in a deep
enough quench the front propagation is governed by linear processes, but the
crystal lattice spacing is determined by nonlinear terms. The wavelength
mismatch can result in significant disorder behind the front that may or may
not persist in the latter stage dynamics. We support these observations by
presenting results from dynamical density functional theory calculations for
simple one- and two-component two-dimensional systems of soft core particles.Comment: 25 pages, 11 figure
The Northern Cross Fast Radio Burst project - II. Monitoring of repeating FRB 20180916B, 20181030A, 20200120E and 20201124A
In this work we report the results of a nineteen-month Fast Radio Burst
observational campaign carried out with the North-South arm of the Medicina
Northern Cross radio telescope at 408~MHz in which we monitored four repeating
sources: FRB20180916B, FRB20181030A, FRB20200120E and FRB20201124A. We present
the current state of the instrument and the detection and characterisation of
three bursts from FRB20180916B. Given our observing time, our detections are
consistent with the event number we expect from the known burst rate ( above our 10, 38~Jy~ms detection threshold) in the 5.2 day active
window of the source, further confirming the source periodicity. We detect no
bursts from the other sources. We turn this result into a 95\% confidence level
lower limit on the slope of the differential fluence distribution to
be and for FRB20181030A and FRB20200120E
respectively. Given the known rate for FRB20201124A, we expect
bursts from our campaign, consistent with our non-detection.Comment: MNRAS Accepted, 10 pages, 6 figure
Incorporating weekly carboplatin in anthracycline and paclitaxel-containing neoadjuvant chemotherapy for triple-negative breast cancer: propensity-score matching analysis and TIL evaluation
Background The generation of data capturing the risk-benefit ratio of incorporating carboplatin (Cb) to neoadjuvant chemotherapy (NACT) for triple-negative breast cancer (TNBC) in a clinical practice setting is urgently needed. Tumour-infiltrating lymphocytes (TILs) have an established role in TNBC receiving NACT, however, the role of TIL dynamics under NACT exposure in patients receiving the current standard of care is largely uncharted. Methods Consecutive TNBC patients receiving anthracycline-taxane [A-T] +/- Cb NACT at three Institutions were enrolled. Stromal-TILs were evaluated on pre-NACT and residual disease (RD) specimens. In the clinical cohort, propensity-score-matching was used to control selection bias. Results In total, 247 patients were included (A-T = 40.5%, A-TCb = 59.5%). After propensity-score-matching, pCR was significantly higher for A-TCb vs A-T (51.9% vs 34.2%, multivariate: OR = 2.40, P = 0.01). No differences in grade >= 3 haematological toxicities were observed. TILs increased from baseline to RD in the overall population and across A-T/A-TCb subgroups. TIL increase from baseline to RD was positively and independently associated with distant disease-free survival (multivariate: HR = 0.43, P = 0.05). Conclusions We confirmed in a clinical practice setting of TNBC patients receiving A-T NACT that the incorporation of weekly Cb significantly improved pCR. In addition, A-T +/- Cb enhanced immune infiltration from baseline to RD. Finally, we reported a positive independent prognostic role of TIL increase after NACT exposure
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