Four waves of Coronavirus disease 2019 (COVID-19) occurred in France between March 2020 and September 2021. COVID-19 inpatient characteristics change because of the influence of numerous parameters, ...especially immunization and circulating severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2) variants.
This retrospective single-center study analyzed patients with laboratory-proven COVID-19 admitted from 1/3/2020 to 30/6/2020 (wave one), 1/7/2020 to 31/12/2020 (wave two), 1/1/2021 to 30/6/2021 (wave three), and 1/7/2021 to 30/11/2021 (wave four). We compared the outcomes and baseline characteristics between these waves.
In our center, 1,762 patients were hospitalized for COVID-19: 666 (37.8 %), 425 (24.1 %), 482 (27.3 %), and 189 (10.7 %) during waves 1, 2, 3, and 4, respectively. Patients during the first wave were hospitalized later after the onset of COVID-19 symptoms, had more severe disease conditions at baseline, and suffered higher intensive care unit (ICU) hospitalization rates. Most patients from waves 1-3 were >70 years old, with 88-93 % having ≥1 comorbidity, whereas those from wave four were younger (68.0 years) with less comorbidities. The first two waves showed higher mortality rates (16.8 % and 20.0 %) than the latter (16.6 % and 9.5 %).
Patients during the first wave had more severe disease conditions at baseline and higher mortality and ICU hospitalization rates. Despite the more virulent circulating Delta variant during wave four, the death and hospitalization rates were markedly decreased during wave four. HIPPOKRATIA 2023, 27 (1):1-6.
Two COVID-19 epidemic waves occurred in France in 2020. This single-center retrospective study compared patients' characteristics and outcomes.
We included all patients with confirmed COVID-19 ...admitted to Colmar Hospital in March (n=600) and October/November (n=205) 2020.
Median ages, sex ratio, body mass index, and number of comorbidities were similar in wave 1 and 2 patients. Significant differences were found for temperature (38°C vs. 37.2), need for oxygen (38.6% vs. 26.8%), high-flow cannula (0% vs. 8.3%), and steroid use (6.3% vs. 54.1%). Intensive care unit (ICU) hospitalizations (25.5% vs. 15.1%, OR: 0.44, 95% CI 0.28; 0.68, P=0.002) and deaths (19.2% vs. 12.7%, OR: 0.61, 95% CI 0.37; 0.98, P=0.04) decreased during the second wave. Except for cardiovascular events (5.5% vs. 10.2%), no change was observed in extrapulmonary events.
Deaths and ICU hospitalizations were significantly reduced during the second epidemic wave.
•The activation volume of Zr46Cu38Ag8Al8 in high-temperature deformation is 284–329Å3.•The S parameter of Zr46Cu38Ag8Al8 is 0.2, same with Zr65Al10Ni10Cu15.•The power dissipation map of ...Zr46Cu38Ag8Al8 exhibited it has excellent workability.
The high temperature rheological behaviors of Zr46Cu38Ag8Al8 and Cu46Zr45Al7Y2 bulk metallic glasses in supercooled liquid region have been investigated by uniaxial strain rate jump compression tests. The results indicate that the high temperature rheological behaviors are sensitive to strain rate and temperature. The rheological behavior will transform from non-Newtonian flow to Newtonian flow with the decrease of strain rate as well as the increase of temperature, which can be explained in the framework of transition state theory. And the rheological behavior of Zr46Cu38Ag8Al8 bulk metallic glass in high temperature is better than that of Cu46Zr45Al7Y2 bulk metallic glass. In addition, the parameter S of both metallic glasses are in a middle level compared with typical bulk metallic glasses, which shown that the metallic glass has an excellent formability in its supercooled liquid region. The optimum domain for thermal workability of these alloys in supercooled liquid region have been roughly located by the deformation map and the power dissipation map, in which the power dissipation efficiency is larger than 0.8. The larger area of optimum domain in the power dissipation map of Zr46Cu38Ag8Al8 exhibited that this bulk metallic glass presents an excellent workability in its supercooled liquid region, but the workability of Cu46Zr45Al7Y2 is not as good as Zr46Cu38Ag8Al8.
A Metallic Glass/Alloy (MeGA) rod with a core in zirconium-based bulk metallic glass and a sleeve in aluminium alloy has been successfully elaborated by co-extrusion. SEM observations of the ...cross-section of the rod show that the interface between the glass and the alloy is defect-free. Compression tests are carried out at room temperature on the MeGA rods containing various glass volume fractions. The yield stress is well described by the rule of mixtures which combines the strength of the glass and that of the alloy, suggesting isostrain behaviour as could be expected. During compression, a good mechanical bonding is observed in the MeGA-rod even after the first fracture of the metallic glass. Finally, push-out tests are performed to evaluate the bonding quality between the two materials. Large values of the shear strength are measured which confirms that co-extrusion leads to good bonding between the glass and the aluminium alloy.
► Elaboration of multi materials associating metallic glasses and conventional crystalline alloys by co-deformation performed at temperatures close to the glass transition temperature of the metallic ...glasses. ► Elaboration of filamentary metal matrix composites with a core in metallic glass by co extrusion. ► Sandwich structures produced by co-pressing. ► Detection of atomic diffusion from the glass to the crystalline alloys during the processes. ► Good interfaces between the metallic glasses and the crystalline alloys, as confirmed by mechanical characterisation.
Multi materials, associating zirconium based bulk metallic glasses and crystalline metallic alloys like magnesium alloys or copper are elaborated by co-deformation processing performed in the supercooled liquid regions (SLR) of the bulk metallic glasses. Two processes are investigated: co-extrusion and co-pressing. In the first case, filamentary composites with various designs can be produced whereas in the second case sandwich structures are obtained. The experimental window (temperature, time) in which processing can be carried out is directly related to the crystallisation resistance of the glass which requires getting information about the crystallisation conditions in the selected metallic glasses. Thermoforming windows are identified for the studied BMGs by thermal analysis and compression tests in their SLR. The mechanical properties of the produced multi materials are investigated thanks to specifically developed mechanical devices and the interfaces between the amorphous and the crystalline alloys are characterised.
Metallic glass/light alloy (MEGA) multilayered materials are elaborated by co-pressing at high temperature. They constitute a layer of Zr-based bulk metallic glass inserted between two layers of ...either aluminium or magnesium alloys. The co-pressing tests are performed at various temperatures above the glass transition temperature of the glass under inert gas. The selected conditions for co-pressing are chosen from the knowledge of the rheological behaviour (deduced from strain rate jump tests) of both the metallic glass and the light alloys and also from information concerning the thermal stability of the glass. It is shown that the bonding between the metallic glass and the light alloys is improved by increasing the strain undergone by the glass during the process. Bonding is also improved by increasing co-pressing temperature, keeping in mind that the amorphous structure of the glass must also be preserved during the process.
High-temperature deformation of a ZrTiCuNiBe bulk metallic glass (BMG) is investigated by compression tests in the supercooled liquid region. When the temperature is decreased or strain rate ...increased, the amorphous alloy exhibits the usual Newtonian/non-Newtonian transition behaviour. Using specific heat treatments, partially crystallized alloys are produced, the associated microstructures characterized and the volume fractions of the crystal measured. The interaction between high-temperature deformation and crystallization is investigated by appropriate mechanical testing. According to these measurements, partial crystallization is responsible for a significant increase in flow stress and the promotion of non-Newtonian behaviour. Deformation does not significantly change the volume fraction, composition or size of the crystal. The flow-stress increase with crystallization is analyzed under different hypotheses. We conclude that the flow-stress increase cannot be interpreted through a compositional change in the residual amorphous matrix, either by reinforcement due to hard crystallites or by connections between crystals. It appears that the effect is due to the nanometric size of the crystals alone.
It is well known that nickel-free zirconium-based bulk metallic glasses are of interest for their possible good biocompatibility properties. In this framework, a Zr–Nb–Cu–Al–Fe bulk metallic glass ...was elaborated under the form of 2
mm diameter rods. The amorphous structure was confirmed by XRD and DSC and the associated reduced index were measured. The mechanical properties of the glass were investigated at both room and high temperature. At room temperature, the glass exhibits some macroscopic plasticity. The rheology at high temperature was studied by both strain rate jump tests and tests at constant strain rate. From these tests, it was difficult to identify an experimental window in which the amorphous structure could be maintained and in which viscoplastic forming could be carried out under low flow stresses. In the super-cooled liquid region, this behaviour is discussed in relation with the resistance to crystallization of the investigated glass and the nature of the formed crystallites was studied by XRD. The mechanical properties of this glass are also compared to results previously obtained in the case of other zirconium-based bulk metallic glasses.
The plastic behaviour of amorphous, partially and totally crystallized Zr
41.25Ti
13.75Cu
12.5Ni
10Be
22.5 (at.%) Vitreloy1 samples is investigated using self similar instrumented indentation. ...Residual imprints are imaged using atomic force microscopy (AFM). Young's modulus and hardness are estimated using the value of the contact area derived from AFM imaging. Compressive tests and three point bending ultrasonic measurements are performed to probe the macroscopic properties. Despite a significant change in the shape of the imprint during the loading, we show that the amorphous alloy does not exhibit any size effect. Both for the amorphous and for the partially crystallized samples, the values of the Young modulus and the yield stress obtained by nanoindentation are consistent with those obtained by the macroscopic procedure. Inversely, the full crystallization samples display high brittleness on compressive tests while no cracking but only an increasing yield stress are observed using indentation. It is concluded that indentation is a well-suited test to probe the mechanical properties of the bulk metallic glasses.
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