Instantaneous Decrease Research Articles

Exports, Productivity and Factor Intensity: Evidence for Brazilian Firms

Based on the theory of heterogeneous firms, participation in the international market leads to changes in performance and efficiency gains at the firm level. This article uses microdata at the level of firms of the Brazilian manufacturing industry (2007-2014) to investigate the impacts of exporting on the productivity trajectory and intensity of factors. The empirical strategy, via Differences in Differences, explores the fact that firms enter at different moments into the external market, generating a variation in the period and in the intensity of the permanence. The results evidence learning effects and the use of comparative advantages so that firms that start exporting have an immediate productivity growth of around 5% and an instantaneous decrease in capital intensity (2.3%) in relation to the pre-entry period compared to non-exporting firms in the comparison group. The permanence on the activity intensifies the effects, so that, after four periods, the growth (reduction) in productivity (intensity of capital) is, approximately, 12% (15%). Among the sources of heterogeneities investigated, the magnitude of effects varies in dimensions such as size, technological intensity and pre-entry levels of productivity and capital intensity.

BIOMECHANICAL STUDY OF PEDICLE SCREW FIXATION STRENGTH: ASSOCIATION OF SCREW MALPOSITION AND SCREW INSERTION TORQUE

Pedicle screws have been widely used for the treatment of spinal diseases, but improper screw placement is not uncommon and may lead to neurovascular injuries and reduced screw fixation strength. This study aimed to investigate the feasibility of using real-time screw insertion torque monitoring to prevent screw penetration. Commercially available synthetic L4 vertebrae were divided in to seven test groups based on different screw placements. Screw insertion torque and maximal pullout strength were compared among groups. The results indicated that the insertion torque gradually increased when the screw tip was within vertebral cancellous bone without penetration. However, an instantaneous decrease of torque value was observed once the screw tip penetrated the cortex wall. When compared to the control group, higher pullout strength was found for the groups with medial cortex penetration. However, vertebrae with medial cortex penetration may lead to the concern of neurovascular damage. Meanwhile, lower pullout strength was found for the groups with lateral cortex penetration and end-plate penetration, which may lead to the concern of screw loosening. We concluded that pedicle screw penetration can be judged using real-time screw insertion torque monitoring during surgery, which may aid surgeons in avoiding neurovascular injury and reduction of screw fixation strength.

Hygro-mechanical response of oak wood cabinet door panels under relative humidity fluctuations

Indoor climate fluctuations are regarded as one of the major risks for the emergence of damage in historical works of art. For a safe preservation of their art objects museums try to minimize this risk, which is typically done by imposing strict limitations on the indoor temperature and humidity conditions. The high energy demand resulting from this approach, however, undermines the aim of preeminent museums to execute a sustainable preservation strategy of their collections. A rational improvement of this aspect asks for detailed information on the history of museum objects, complemented by a thorough comprehension of the failure and deformation behaviour of museum objects under indoor climate fluctuations. Accordingly, in this paper the hygro-mechanical response of mock-ups of historical Dutch cabinet door panels made of oak wood is examined under several relative humidity variations. In specific, the mock-ups were subjected to (i) an instantaneous decrease of 40% relative humidity, (ii) eight successive, instantaneous drops of 5% relative humidity, and (iii) a varying relative humidity profile ranging between 35 and 71%. The shrinkage characteristics of mock-ups are translated to their damage susceptibility using an analytical hygro-mechanical bi-layer model. This model shows that restrained hygral shrinkage may originate from: (i) a difference in moisture content across the thickness direction of the panel, or (ii) a directional difference in the coefficient of hygroscopic expansions of structural components forming a coherent connection. The first type of shrinkage occurs in the outer regions of the panel thickness, while the second type of shrinkage takes place at the cleated ends. Further, by accounting for the age-dependency of the fracture strength of oak wood, a clear distinction can be made between the damage susceptibility of new door panels and historical door panels present in museum cabinets. The six main conclusions of the experimental study—conveniently summarized at the end of this paper—provide a scientific basis for the understanding of shrinkage cracks and dimensional changes observed on decorated oak wooden panels in historical Dutch cabinets, and thus may assist in advising museums on future sustainable preservation strategies and rational guidelines for indoor climate specifications.

Optimal System Design and Sequential Preventive Maintenance Under Uncertain Aperiodic-Changing Stresses

This paper presents a two-stage stochastic programming model with recourse for integrating the design and sequential preventive maintenance schedule of a system, which is subject to uncertain aperiodic-changing future usage stresses. Specifically, the usage stresses change as the system operates and preventive maintenance is conducted. The system undergoes imperfect repair according to the sequential preventive maintenance policy and minimal repair in response to emergency failures. The system is replaced when the maintenance is uneconomical due to the deterioration of the components. Under such future usage stresses and maintenance, this paper formulates the failure rates and lifetime distributions of components and the system, the failure rates increase with the usage stresses, and both the failure rates and usage stresses have an instantaneous incremental decrease at each preventive maintenance action. In the two-stage stochastic optimization model, the first-stage decision variables are the numbers of components to be used in the subsystems, and these variables affect the second-stage variables, which define the number of imperfect preventive maintenance actions before the replacement of the system and the aperiodic preventive maintenance time intervals for various future usage scenarios. Analytical properties about the failure rates of components and subsystems and the solution for minimizing expected system maintenance cost rate are derived. A decomposition method for solving the proposed two-stage stochastic model is designed based on the analytical results. Numerical examples and sensitivity analysis are provided for deep understanding of the proposed method.

Effect of Welding Speed on Fatigue Properties of TC18 Thick Plate by Electron Beam Welding

The welding of 15 mm thick TC18 titanium alloy thick plate was realized by electron beam welding. The effect of different welding speeds (10, 20, 30 mm/s) on the fatigue properties of the electron beam welded joints for TC18 titanium alloy was investigated. The macroscopic morphology, microstructure and fracture characteristics of the joints were analyzed by optical microscope, scanning electron microscopy and transmission electron microscopy, and the fatigue properties of welded joints were studied and tested by an electronic universal testing machine. The results show that the weld fusion zone is mainly composed of columnar β phase and acicular α martensite phase. The upper melting width, the middle melting width and the lower melting width are obviously reduced, and the grain size gradually decreases with the increase of welding speed, which results in the increase of fatigue properties of welded joints. At Nf =107 the fatigue limit of the weld increases by nearly 29% with the welding speed from 10 mm/s to 30 mm/s. The fatigue fracture of the joints can be divided into three typical regions of fatigue crack source zone, expansion zone and instantaneous zone, and the fatigue cracks all originate from the surface of the specimen. With the increase of welding speed, the proportion of instantaneous area decreases and the fatigue performance increases.

Автономный однофазный инвертор с высоким качеством выходного напряжения

The solution of the relevant problem of improving the quality of the output signal of autonomous voltage inverters is presented. In contrast to the pulse width modulation (PWM) traditionally used for this purpose, a topology containing a single-phase bridge inverter and a direct-current source switch at the input is proposed, which makes it possible to form an eight-step voltage with a total harmonic coefficient of 6.9% on the load, which meets the requirements of modern standard on the quality of electricity. The novelty of the technical solution is confirmed by the utility model patent. The optimization of the curve of the multistage signal approximating the sinusoid, using the minimum harmonic coefficient criterion, was carried out with the help of evolutionary modeling (genetic algorithm). The study of electromagnetic processes was carried out by the method of simulation. The received results confirmed the invariance of the harmonic coefficient of the inverter output voltage throughout the range of the load power factor variation 0 ≤ cos φ ≤ 1 and the stability of the system with instantaneous increase and decrease of the load. The importance of the proposed and investigated circuit solution is determined by the advantages of step modulation in comparison with the pulse-width modulation: – low dynamic losses in key elements, allowing the inverter to be used in a wide frequency range; – independence of the harmonic coefficient on the frequency and nature of the load; – reduction of mass-dimensional parameters, due to the lack of the need to install a filter at the output of the inverter, because the guaranteed quality of electricity meets the requirements of the standard; – in comparison with the method of pulse-width modulation, absence of a negative influence on the characteristics of consumers and the terms of their operation, if no higher-harmonic filters are used. The scope of the above inverter circuit includes radioelectronic equipment, communication equipment, electric drives. The greatest advantages of the proposed circuit solution are manifested when the inverter is connected to the local power supply system with renewable energy sources (solar panels, batteries), since in this case the installation of galvanically isolated rectifiers as the sources of direct current at the input of the AIN is not necessary.

A novel lab-on-a-chip platform for spheroid metabolism monitoring.

Sensor-based cellular microphysiometry is a technique that allows non-invasive, label-free, real-time monitoring of living cells that can greatly improve the predictability of toxicology testing by removing the influence of biochemical labels. In this work, the Intelligent Mobile Lab for In Vitro Diagnostics (IMOLA-IVD) was utilized to perform cellular microphysiometry on 3D multicellular spheroids. Using a commercial 3D printer, 3×3 microwell arrays were fabricated to maintain nine previously cultured HepG2 spheroids on a single BioChip. Integrated layers above and under the spheroids allowed fluidic contact between spheroids in microwells and BioChip sensors while preventing wash out from medium perfusion. Spheroid culturing protocols were optimized to grow spheroids to a diameter of around 620μm prior to transfer onto BioChips. An ON/OFF pump cycling protocol was developed to optimize spheroid culture within the designed microwells, intermittently perfuse spheroids with fresh culture medium, and measure the extracellular acidification rate (EAR) and oxygen uptake rate (OUR) with the BioChips of the IMOLA-IVD platform. In a proof-of-concept experiment, spheroids were perfused for 36h with cell culture medium before being exposed to medium with 1% sodium dodecyl sulphate (SDS) to lyse cells as a positive control. These microphysiometry studies revealed a repeatable pattern of extracellular acidification throughout the experiment, indicating the ability to monitor real-time metabolic activity of spheroids embedded in the newly designed tissue encapsulation. After perfusion for 36h with medium, SDS exposure resulted in an instant decrease in EAR and OUR signals from 37mV/h (±5) to 8mV/h (±8) and from 308mV/h (±21) to -2mV/h (±13), respectively. The presented spheroid monitoring system holds great potential as a method to automate screening and analysis of pharmaceutical agents using 3D multicellular spheroid models.

Numerical investigation on the oscillating flow and uneven heat transfer processes of the cooling oil inside a piston gallery

In previous research of achieving high cooling efficiency of engine pistons, the phenomenon of uneven heat transfer has not been investigated or recognized. These issues lead to a greater piston temperature gradient and its effects on engine durability have not been paid sufficient attention. In this research, a piston gallery was classified into four regions and several zones per region to investigate oscillating oil flows and uneven heat transfer distributions with a Relative Displacement Method (RDM). The RDM allows the cooling gallery to be treated as a rigid body, and the original constant boundary conditions could be translated into varying conditions that change as a function of engine crank angle. The relationships are investigated between the heat transfer performance and some factors such as the movement conditions of the air-oil two-phase flow inside the gallery, the instantaneous oil distributions, the relative oil velocity, the instantaneous acceleration and the velocity of the piston. The results reveal that the instantaneous oil charge ratio decreases and the area-weighted heat transfer coefficient increases as the engine speed increases. Different regions exhibit more apparent uneven heat transfer at higher engine speeds, and the top and bottom regions play a dominant role in the overall heat transfer coefficient. When the gallery was positioned closer to the oil inlet passage, the uneven heat transfer is more intense.

Nanosecond electric pulses differentially affect inward and outward currents in patch clamped adrenal chromaffin cells.

This study examined the effect of 5 ns electric pulses on macroscopic ionic currents in whole-cell voltage-clamped adrenal chromaffin cells. Current-voltage (I-V) relationships first established that the early peak inward current was primarily composed of a fast voltage-dependent Na+ current (INa), whereas the late outward current was composed of at least three ionic currents: a voltage-gated Ca2+ current (ICa), a Ca2+-activated K+ current (IK(Ca)), and a sustained voltage-dependent delayed rectifier K+ current (IKV). A constant-voltage step protocol was next used to monitor peak inward and late outward currents before and after cell exposure to a 5 ns pulse. A single pulse applied at an electric (E)-field amplitude of 5 MV/m resulted in an instantaneous decrease of ~4% in peak INa that then declined exponentially to a level that was ~85% of the initial level after 10 min. Increasing the E-field amplitude to 8 or 10 MV/m caused a twofold greater inhibitory effect on peak INa. The decrease in INa was not due to a change in either the steady-state inactivation or activation of the Na+ channel but instead was associated with a decrease in maximal Na+ conductance. Late outward current was not affected by a pulse applied at 5 MV/m. However, for a pulse applied at the higher E-field amplitudes of 8 and 10 MV/m, late outward current in some cells underwent a progressive ~22% decline over the course of the first 20 s following pulse exposure, with no further decline. The effect was most likely concentrated on ICa and IK(Ca) as IKV was not affected. The results of this study indicate that in whole-cell patch clamped adrenal chromaffin cells, a 5 ns pulse differentially inhibits specific voltage-gated ionic currents in a manner that can be manipulated by tuning E-field amplitude.

Borrowers in Search of Feedback: Evidence from Consumer Credit Markets

We study recent technological innovation in credit markets and document their role in providing information to households. We show that households value the ability to learn detailed information about their cost of credit. This function is most valued by less creditworthy households with less experience in credit markets. To measure the demand for information provision we exploit a quasi-natural experiment in an online consumer credit market. A large lending platform unexpectedly switched from pricing loans through an auction mechanism to centralized pricing determined by broad credit grade. This change resulted in an instant decrease in the amount of tailored feedback available to market participants. We find that less experienced households immediately and disproportionately exit the market and the response is concentrated among higher risk households. We rule out alternative explanations such as changes in access to credit, borrower risk profiles, and interest rate levels. Our findings point to a potentially important role for financial innovation: enabling less experienced households to more easily learn about their credit market options.

Experimental Platform for Operational Analysis of Distribution Networks

The benefits provided by changes of topology are essentials to better use of all electrical system elements. In some situations, it can be observed that the load transfer results in an instant decrease of losses along of network, providing the balancing of voltage levels, becoming the network more robust. Thus, this paper presents an analysis of the applicability of optimization methods of networks using an experimental platform, developed and tested in a controlled environment.

Numerical modelling of the deterioration of the Parisian metro infrastructures based on a new auscultation method

Many underground transport systems have aged and need heavy maintenance. Most of these tunnels have been affected by diverse weathering processes that have led to superficial or deep deterioration of the structure. To schedule maintenance operations, managers of these infrastructure networks need to assess the current state of tunnels. However, current diagnostic methods are mainly based on visual observations that cannot completely characterise the current state of these structures and predict the kinetics of degradation and its effect on the structural behaviour over time. In this context, we propose a methodology designed to obtain a state of deterioration of infrastructures and their evolution over time by integrating different parameters into the geometry of the tunnels and the value of the mechanical parameters of each zone (tunnel components and the ground). A numerical modelling procedure based on the parameters derived from a new methodology for auscultation is used to highlight the most damaged areas, which can disrupt the stability of the underground structures. The instantaneous decrease in the mechanical parameters of galleries is considered (from the initial state) to reproduce different states of alteration displayed on different surveys. Several scenarios are proposed to indicate the possible degradation observed on this underground.

Suvremeni demografski i razvojni izazovi općine Dubrovačko primorje, Hrvatska

The purpose of this paper is to define the basic issues and opportunities challenging the modern development of the Municipality of Dubrovačko Primorje, their causes and effects. The processes of depopulation affected this poorly developed rural region since 1960s, which had been influenced by various factors: development polarisation caused by intensive development of tourism, the poor traffic infrastructure in the highland-area of the Municipality and the unsolved water supply issue. In 1990s a series of events intensified negative demographic trends as follows: aggression on Croatia, occupation during which residential, economic and infrastructural buildings were destroyed and burnt, as well as an earthquake which happened after the return of the refugees. The long-lasting rural emigration from this region towards Dubrovnik caused not only an instantaneous decrease of population but also a contraction of the renewing basis and an accelerated decrease of natural growth in the Municipality of Dubrovačko Primorje. In that way the emigrational depopulation as a consequence of a specific socioeconomic development, became the cause of the current biological depopulation. The intensity of the depopulation processes has been established by an analysis of a total population dynamics and the changes in biological and economic population structure. The conclusion of the study indicates activities which have promising development in the Municipality of Dubrovačko Primorje and which might partly stop the negative demographic trends. Those are mainly traditional activities in this region which are not commercially used enough. They should prevent any further emigration and perhaps even attract those who immigrated, back to their place of birth

Role of vagus in mediating the toxicity induced by Mesobuthus tamulus venom in rats

Background: Mesobuthus tumulus (red scorpion, MBT) envenomation is a serious health problem in tropical countries and is responsible for high morbidity and mortality. Aims and Objectives: Earlier reports about the role of vagus in producing MBT venom-induced toxicity are conflicting. Therefore, in this study, the role of vagus in MBT venom-induced toxicity in rats was evaluated. Materials and Methods: The rats were divided into three groups. In group I, only saline was injected. This group served as control. In group II, MBT venom was injected. In group III, MBT venom was injected in vagotomized rats. Mean arterial pressure (MAP), ECG (for heart rate [HR]), respiratory rate, pulmonary water content, and survival time were determined in all groups. Results: Exposure to MBT venom in rats produced prolonged apnea with intermittent shallow breathing and was accompanied by an instantaneous decrease, followed by an increase and then a progressive decrease in MAP and HR leading to death within 60 min. There was increased pulmonary water content (82% vs. 74% in controls). MBT venom in vagotomized rats produced immediate changes as before, but these changes recovered to reasonably good level within 30 min and the animals survived for >120 min. Pulmonary water content in vagotomized rats was similar to control group. Conclusion: The results indicate that vagus plays a vital role for the toxic effects produced by MBT venom.

Salusins in Hypertension and Related Cardiovascular Diseases.

The salusins are bioactive peptides with hemodynamic effects. They play a role in hypertension, atherogenesis and cardiovascular diseases. In this review we focus on new actions, which are related to the regulation of blood pressure. Decrease in salusin-̛ and the increase in salusin-̜ concentrations are known to contribute to the development of the metabolic syndrome and atherosclerosis. Microinjections of salusin-̜. in the paraventricular nucleus (PVN) increases the plasma argininevasopressin (AVP) and norepinephrine levels, which contribute to hypertension. It also increases the AVP release from the rostral ventrolateral medulla (RVLM) via the projection from PVN to RVLM. Increased activity of the RVLM neurons is transmitted to the intermediolateral nucleus (IML) cell column of the spinal cord, where peripheral sympathetic nerves to the heart, arterioles and kidneys are activated, thus increasing blood pressure. Microinjection of salusin-̜ into the RVLM increased renal sympathetic nerve activity, median arterial pressure (MAP) and heart rate (HR). There was no significant effect on the AVP level in the RVLM and plasma. Microinjection of salusin-̜. in the nucleus tractus solitarii (NTS) produces a dose dependent hypotension and bradycardia. Intravenous injection of salusin-̜. significant increased MAP, but did not have a meaningful outcome on HR. Nevertheless, intravenous injection of a very high dose of salusin-̜. caused instantaneous decrease in both MAP and HR. Salusin-̜. overexpression provoked severe and prolonged hypertension accompanied by tachycardia in rats. It is clear that more research needs to be done to evaluate the function of salusin-̜ in the mechanism of essential hypertension, atherosclerosis, and the metabolic syndrome.

Cross-frequency information transfer from EEG to EMG in grasping.

This paper presents an investigation into the cortico-muscular relationship during a grasping task by evaluating the information transfer between EEG and EMG signals. Information transfer was computed via a non-linear model-free measure, transfer entropy (TE). To examine the cross-frequency interaction, TEs were computed after the times series were decomposed into various frequency ranges via wavelet transform. Our results demonstrate the capability of TE to capture the direct interaction between EEG and EMG. In addition, the cross-frequency analysis revealed instantaneous decrease in information transfer from EEG to the high frequency component of EMG (100-200Hz) during the onset of movement.

Role of the boundary layer dynamics effects on an extreme air pollution event in Paris

The physical and chemical aerosol properties are explored here based on ground-based observations in the Paris region to better understand the role of clouds, radiative fluxes and dynamics on aerosol loading during a heavy regional air pollution that occurred in March 2014 over North-Western Europe. This event is primarily characterized by a fine particle mass (PM2.5) increase from 10 to more than 120 μg m−3 and a simultaneous decrease of the horizontal visibility from 40 to 1 km, mainly due to significant formation of ammonium nitrate particles. The aerosol optical depth (AOD) at 550 nm increased steadily from about 0.06 on March 6 to more than 0.9 five days later. The scattering of the solar radiation by polluted particles induced, at the peak of the heavy pollution event, an instantaneous shortwave flux decrease of about 300 W m−2 for direct irradiance and an increase of about 150 W m−2 for diffuse irradiance (only scattering). The mean surface aerosol effect efficiency (effect per unit optical depth) is of about −80 W m−2 with a mean aerosol direct radiative effect of −23 W m−2. The dynamical and radiative processes that can be responsible for the diurnal cycle of PM2.5 in terms of amplitude and timing are investigated. A comparative analysis is performed for 4 consecutive days (between March 11 and 14), showing that the PM2.5 diurnal cycle can be modulated in time and amplitude by local processes such as the boundary layer depth development (ranging from 100 m to 1350 m), surface relative humidity (100%–35%), thermal structure (10 °C–16 °C for day/night amplitude), dynamics (wind speed ranging from 4 m s−1 to 1.5 m s−1) and turbulence (turbulent kinetic energy reaching 2 m2 s−2) near the surface and wind shear along the vertical. Finally, modeled and measured surface PM2.5 loadings are also compared here, notably illustrating the need of accurate boundary layer depth data for efficient air quality forecasts.

Sensitivity to Auditory Velocity Contrast.

A natural auditory scene often contains sound moving at varying velocities. Using a velocity contrast paradigm, we compared sensitivity to velocity changes between continuous and discontinuous trajectories. Subjects compared the velocities of two stimulus intervals that moved along a single trajectory, with and without a 1 second inter stimulus interval (ISI). We found thresholds were threefold larger for velocity increases in the instantaneous velocity change condition, as compared to instantaneous velocity decreases or thresholds for the delayed velocity transition condition. This result cannot be explained by the current static “snapshot” model of auditory motion perception and suggest a continuous process where the percept of velocity is influenced by previous history of stimulation.

The Effect of Short Duration Electric Current on the Quasi-Static Tensile Behavior of Magnesium AZ31 Alloy

The effect of a single pulse of electric current with short duration on the quasi-static tensile behavior of a magnesium AZ31 alloy is experimentally investigated. A single pulse of electric current with duration less than 1 second is applied to the specimen, while the specimen is being deformed in the plastic region under quasi-static tensile loads. After a nearly instant decrease of flow stress at the pulse of electric current, the flow stress shows strain hardening until the failure of the specimen. The experimental result shows that the strain-hardening parameters (the strength coefficient and the strain-hardening exponent) of the hardening curve after the electric current strongly depend on the applied electric energy density (electric energy per unit volume). Empirical expressions are suggested to describe the hardening behavior after the pulse as a function of the electric energy density and are compared with the empirical expressions suggested for advanced high-strength steels.

Instantaneous Decrease in Left Ventricular Afterload during Transcatheter Aortic Valve Implantation Results in Immediate Changes in Left Ventricular Strain.

Severe aortic stenosis causes chronic increased afterload on the left ventricle (LV) resulting in myocardial hypertrophy and ultimately dysfunction if left untreated. Transcatheter aortic valve implantation (TAVI) immediately decreases the afterload on the LV by reducing the pressure gradient through the aortic valve. In our study, we aim to evaluate immediate changes in LV mechanics using intra-procedural transesophageal echocardiography (TEE) to assess circumferential and radial strain via speckle tracking. Intra-operative TEE was performed during TAVI for 53 patients (mean age 84 ± 8 years). Two-dimensional images in the transgastric view were acquired at the level of the papillary muscle. Circumferential and radial strain was calculated using speckle tracking with Philips Qlab software. Global LV afterload was measured by calculating valvulo-arterial impedance (Zva). Immediately post-TAVI, there was a change in both radial strain rate (Pre: 0.73 ± 0.04 vs. Post: 0.88 ± 0.04 per second, P < 0.001) and circumferential strain rate (-0.53 ± 0.04 (pre) vs. -0.74 ± 0.04 (post) per second, P < 0.001). There was also an immediate improvement in circumferential global strain parameters (-14.5 ± 5% (pre) vs. -16.0 ± 4.7% (post), P < 0.05), whereas there was no significant change seen in global radial strain (15.6 ± 0.8% (pre) vs. 15.2 ± 0.9% (post), P = 0.69). No significant change was seen in LV ejection fraction (51.5 ± 14.2% (pre) vs. 52.1 ± 14.0% (post), P = 0.77). Speckle tracking using TEE images is feasible and identifies significant improvements in LV strain and strain rate immediately following TAVI that is not detected by conventional measure of LV function.