SARS-CoV-2 is the virus that causes coronavirus disease (COVID-19) which has reached pandemic levels resulting in significant morbidity and mortality affecting every inhabited continent. The large ...number of patients requiring intensive care threatens to overwhelm healthcare systems globally. Likewise, there is a compelling need for a COVID-19 disease severity test to prioritize care and resources for patients at elevated risk of mortality. Here, an integrated point-of-care COVID-19 Severity Score and clinical decision support system is presented using biomarker measurements of C-reactive protein (CRP), N-terminus pro B type natriuretic peptide (NT-proBNP), myoglobin (MYO), D-dimer, procalcitonin (PCT), creatine kinase-myocardial band (CK-MB), and cardiac troponin I (cTnI). The COVID-19 Severity Score combines multiplex biomarker measurements and risk factors in a statistical learning algorithm to predict mortality. The COVID-19 Severity Score was trained and evaluated using data from 160 hospitalized COVID-19 patients from Wuhan, China. Our analysis finds that COVID-19 Severity Scores were significantly higher for the group that died
versus
the group that was discharged with median (interquartile range) scores of 59 (40-83) and 9 (6-17), respectively, and area under the curve of 0.94 (95% CI 0.89-0.99). Although this analysis represents patients with cardiac comorbidities (hypertension), the inclusion of biomarkers from other pathophysiologies implicated in COVID-19 (
e.g.
, D-dimer for thrombotic events, CRP for infection or inflammation, and PCT for bacterial co-infection and sepsis) may improve future predictions for a more general population. These promising initial models pave the way for a point-of-care COVID-19 Severity Score system to impact patient care after further validation with externally collected clinical data. Clinical decision support tools for COVID-19 have strong potential to empower healthcare providers to save lives by prioritizing critical care in patients at high risk for adverse outcomes.
The COVID-19 Severity Score combines multiplex biomarker measurements and risk factors in a statistical learning algorithm to predict mortality.
FE model updating techniques are used to update dynamic FE models of structures in the light of modal test data. Iterative methods of model updating that update a set of chosen parameters of the ...model, so as to reduce the difference between the natural frequencies and the mode shapes of the FE model and the corresponding quantities obtained through a modal test on the structure, are probably the most widely used methods. Once experimental modal data has been identified, a necessary prior step, before updating can be carried out, is that of establishing the correspondence between the FE model modes and the experimentally identified modes.
It is however experienced that, many a times a situation is encountered where not all of the modes identified through an experiment can be correlated with certainty with those predicted by the FE model and some experimental modes may be left uncorrelated. There could be several reasons for this lack of correlation as identified in the paper. But the consequence is that such uncorrelated modes cannot be used in FE model updating using existing iterative methods based on modal data even when they form valid known pieces of information about the structure. This is a disadvantage since it reduces the quantity of experimental data available for model updating and hence makes the updating process less effective in yielding an updated model that is a closer representation of the structure.
This paper identifies this as a limitation of the existing iterative methods of model updating based on modal data and puts forward a notion of FE model updating using uncorrelated modes. The paper proposes a solution to overcome this limitation in the form of a new method of FE model updating that accepts both correlated as well as uncorrelated modes for updating. This is in contrast to all the current iterative modal data based methods of model updating that are based on the assumption of availability of correlated mode pairs and hence cannot use uncorrelated mode shapes and corresponding natural frequencies in the updating process. Formulation of the proposed method is described followed by a couple of numerical examples based on a beam structure to validate the method. The robustness of the method in the presence of simulated noise is also studied. Another numerical example of a more complex F-shape structure is also presented. The method is then validated though an experimental study. The proposed method is found to successfully update an FE model yielding correct estimates of the updating parameters in the presence of uncorrelated modes.
We study a junction of a topological insulator with a thin two-dimensional nonmagnetic or partially polarized ferromagnetic metallic film deposited on a three-dimensional insulator. We show, by ...deriving generic boundary conditions applicable to electrons traversing the junction, that there is a finite spin-current injection into the film whose magnitude can be controlled by tuning a voltage V applied across the junction. For ferromagnetic films, the direction of the component of the spin current along the film magnetization can also be tuned by tuning the barrier potential V sub(0) at the junction. We point out the role of the chiral spin-momentum locking of the Dirac electrons behind this phenomenon and suggest experiments to test our theory.
•A two stage approach to updating of mass, stiffness and damping matrices is proposed.•Coupling between the two stages of updating is investigated through a numerical study.•Effect of data ...incompleteness and noise on the coupling between the two stages is investigated.•A hybrid data based approach is suggested to deal with data incompleteness.•Effectiveness of the two-stage approach is studied through an experimental study.
Model updating techniques are used to update a dynamic FE model of a structure so as to obtain its accurate representation in terms of mass, stiffness and damping matrices. Some of the existing updating methods update all the three matrices simultaneously using either complex FRFs or modal data. These methods, however, are faced with numerical problems in practical implementation due to large difference in the magnitudes of the elements of the stiffness and mass matrices on one end and of the damping matrix on the other.
This paper proposes a two-stage approach for updating mass, stiffness and damping matrices and performs numerical and experimental investigations to assess the effectiveness of such an approach. The first stage of updating is based on the concept of normal FRFs, which represent the FRFs of a structure if the structure were undamped, to update the mass and stiffness matrices. In the second stage, the damping matrix is updated based on the difference of complex and normal FRFs, which represents the effect of damping in the structure on its frequency response.
The numerical example of a fixed-fixed beam structure is first considered that allows investigating the impact of first stage of updating on the second stage. This is followed by an experimental example of an F shape structure. A new method called ‘hybrid’ method to deal with data incompleteness in the context of two-stage updating is suggested. Effectiveness of the two-stage method when updating parameters cannot be chosen correctly is also investigated. The two stage approach presented and the results of the investigations carried out would be helpful in proper implementation and application of the proposed updating method in practice.
Display omitted Flow chart of two-stage updating method.
The present work attempts to study the influences of internal rotor material damping and the fluid film forces (generated as a result of hydrodynamic action in journal bearings) on the modal ...behaviour of a flexible rotor-shaft system. This is relevant as both journal bearing and the internal material damping introduce tangential forces increasing with the rotor spin speed. Such forces considerably influence the dynamic behaviour of a rotor and tend to destabilize the rotor-shaft system as spin speed increases. Under this system of forces the modal behaviour of the rotor-shaft is studied to get better ideas about the dynamic behaviour of the system, estimated in terms of modal damping factors, stability limit speed, the frequency response functions, as well as the direction of whirl of the shaft in different modes. It is seen that correct estimation of internal friction, in general, and the journal bearing coefficients at the rotor spin-speed are essential to accurately predict the rotor dynamic behaviour. This serves as a first step to get an idea about dynamic rotor stress and, as a result, a dynamic design of rotors.
► This work presents modal analysis of rotors on journal bearings. ► Rotating damping forces due to bearing and internal friction are considered. ► Rotor mode shapes and whirl directions are also shown. ► Modal damping factors are used to find stability; dFRF used to study response. ► This work serves as the first step to dynamic design of rotor-shaft systems.
Operational Modal Analysis (OMA) is used to extract modal parameters of a structure on the basis of their output response measured during operation. OMA, when applied to mechanical engineering ...structures is often faced with the problem of harmonics present in the output response. A complex structure may have many dominant frequency components in its response frequency spectrum. These may contain frequency components associated with resonant frequencies of the structure, which and the associated mode shapes and the damping factors represent the data of interest, but may also contain frequencies or harmonics associated with the excitation sources. Since in OMA the characteristics of the excitation sources are not known, one of the problems lies in separating the resonant frequencies from the harmonic excitation frequencies. Any error in this regard may lead to an error in modal identification with the consequence that a harmonic may be construed as a structural mode and vice versa. This issue is addressed in this paper and a method is presented for separating resonant frequencies from harmonic excitation frequencies using random decrement of the response. The principle of the method is presented using an analytical study on a single degree of freedom system. The effectiveness of the method is then demonstrated through numerical studies on a lumped parameter multi-degree of freedom system and a simulated plate structure. Detection of single and multiple harmonics in the response that are well separated as well as close to resonant frequencies are considered.
•A method of separation of structural modes from the harmonic frequencies in OMA is proposed.•The method utilizes the difference in the characteristics of randomdec signature of stochastic and harmonic response.•Method works well for well-separated harmonics as well as harmonics close to resonant frequencies.•Method is easy to implement and requires little data.
Accurate modeling of damping in structures is of great importance for vibration response analysis and control. This paper addresses the issue of identification of damping matrix of a structure by ...posing it as a finite element damping matrix updating problem. Many of the current updating approaches, dealing with updating of damping matrix, perform simultaneous updating of mass, stiffness and damping matrices. However, such a strategy is faced with numerical problems in practical implementation, since the magnitude of stiffness and mass matrix elements is generally much more than that of the damping matrix elements causing difficulties in accurate identification of the damping matrix. Some other approaches divide the process of updating of the mass and stiffness matrix and the damping matrix into two stages, but their application is restricted to structures with low levels of damping. This paper addresses these issues by developing an updating formulation that seeks to separate updating of the damping matrix from that of updating of the stiffness and the mass matrix. The proposed damping matrix updating method utilizes the concept of normal frequency response functions (FRFs) available in the literature. The method is formulated so as to reduce the difference between the complex FRFs, which can be measured in practice, and the normal FRFs, whose estimates can be obtained from the measured complex FRFs. The effectiveness of the proposed method is demonstrated through a numerical study on a simple but representative beam structure. The issue of coordinate incompleteness and robustness of the method under presence of noise is investigated. It is found that the proposed method is effective in the accurate identification of the damping matrix in cases of complete, incomplete and noisy data and is not limited by the level of damping in the structure.
► Damping matrix identification through updating of FE damping matrix is proposed. ► Damping matrix updating is separated from stiffness and mass matrix updating. ► Method is based on the concept of normal frequency response functions. ► Method can handle both viscous and structural damping. The method is applicable for any level of damping.
XRD analysis and magnetic measurements were used to study the effect of 80 MeV
16
O
6+
ion-irradiation on structural, magnetic properties, and anti-structural modeling of as-burnt ZnFe
2
O
4
...synthesized by sol-gel auto-combustion technique. XRD confirms the formation of single-phase spinel nanoferrite. Irradiation leads to modification of (i) lattice-parameter; strain; oxygen parameter, Fe
3+
, Zn
2+
ions on A, B site; inversion degree; A-O-B, A-O-A, B-O-B super-exchange-interaction; (ii) saturation magnetization; anisotropy; squareness-ratio; surface dead-layer-thickness. Antistructural modeling describes the surface-active centers for pristine and irradiated samples. Studies reveal strong connection between structural and magnetic properties, useful for ion-irradiation-induced tuning properties of ZnFe
2
O
4
.
We report sol gel auto-combustion synthesized CoCr
x
Fe
2-x
O
4
(
x
= 0.0 − 1.0) spinel ferrites, and use x-ray diffraction ‘XRD’, magnetic measurements, and Mössbauer spectroscopy to study the ...effect of Cr-content on their structural properties, magnetic properties, and correlation between them. Formation of single-phase nono spinel ferrite (grain size: 18.1 – 46.6 nm), is confirmed by XRD. Results show that with increasing Cr-content, lattice parameter decreases, and Cr
3+
ions remain more populated on B-site, whereas Co
2+
ions remains almost equally populated on both A, B site, show lower disorder, and modification of A–O − A, B– O − B, A–O − B super-exchange interaction. For Cr-content ≥ 0.75, Mössbauer measurements show presence of a non-magnetic doublet, and isomer shift values confirm that Fe has 3 + oxidation state. Observed structural changes, lead to reduction of saturation magnetization, coercivity.
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