Improved oxidation behavior of Hf0.11Al0.20B0.69 in comparison to Hf0.28B0.72 magnetron sputtered thin films.

The oxidation resistance of Hf0.28B0.72 and Hf0.11Al0.20B0.69 thin films was investigated comparatively at 700 °C for up to 8 h. Single-phase solid solution thin films were co-sputtered from HfB2 and AlB2 compound targets. After oxidation at 700 °C for 8 h an oxide scale thickness of 31  ±  2 nm was formed on Hf0.11Al0.20B0.69 which corresponds to 14% of the scale thickness measured on Hf0.28B0.72. The improved oxidation resistance can be rationalized based on the chemical composition and the morphology of the formed oxide scales. On Hf0.28B0.72 the formation of a porous, O, Hf, and B-containing scale and the formation of crystalline HfO2 is observed. Whereas on Hf0.11Al0.20B0.69 a dense, primarily amorphous scale containing O, Al, B as well as approximately 3 at% of Hf forms, which reduces the oxidation kinetics significantly by passivation. Benchmarking Hf0.11Al0.20B0.69 with Ti-Al-based boride and nitride thin films with similar Al concentrations reveals superior oxidation behavior of the Hf-Al-based thin film. The incorporation of few at% of Hf in the oxide scale decelerates oxidation kinetics at 700 °C and leads to a reduction in oxide scale thickness of 21% and 47% compared to Ti0.12Al0.21B0.67 and Ti0.27Al0.21N0.52, respectively. Contrary to Ti-Al-based diborides, Hf0.11Al0.20B0.69 shows excellent oxidation behavior despite B-richness.

Neurovascular coupling methods in healthy individuals using transcranial doppler ultrasonography: A systematic review and consensus agreement.

Neurovascular coupling (NVC) is the perturbation of cerebral blood flow (CBF) to meet varying metabolic demands induced by various levels of neural activity. NVC may be assessed by Transcranial Doppler ultrasonography (TCD), using task activation protocols, but with significant methodological heterogeneity between studies, hindering cross-study comparisons. Therefore, this review aimed to summarise and compare available methods for TCD-based healthy NVC assessments. Medline (Ovid), Scopus, Web of Science, EMBASE (Ovid) and CINAHL were searched using a predefined search strategy (PROSPERO: CRD42019153228), generating 6006 articles. Included studies contained TCD-based assessments of NVC in healthy adults. Study quality was assessed using a checklist, and findings were synthesised narratively. 76 studies (2697 participants) met the review criteria. There was significant heterogeneity in the participant position used (e.g., seated vs supine), in TCD equipment, and vessel insonated (e.g. middle, posterior, and anterior cerebral arteries). Larger, more significant, TCD-based NVC responses typically included a seated position, baseline durations >one-minute, extraneous light control, and implementation of previously validated protocols. In addition, complementary, combined position, vessel insonated and stimulation type protocols were associated with more significant NVC results. Recommendations are detailed here, but further investigation is required in patient populations, for further optimisation of TCD-based NVC assessments.

Foliar applications of zinc oxide nanoparticles and boric acid affect leaf oxidative metabolism and productivity in young pecan trees.

Zinc and boron are nutrients that often suffer low bioavailability to pecan trees grown in calcareous soils whereas adequate supplies of these two elements is essential for commercial pecan production. Working with young pecan trees, we evaluated changes in oxidative metabolism, levels of bioactive compounds, yield components and foliar nutrient concentrations in response to foliar sprays (50 or 100 mg L-1) of zinc oxide nanoparticles (ZnO NPs) and boron (H3BO3). Four different treatment solutions were applied in a completely randomised design with six replications per treatment (24 trees in total). Zinc and B treatments were applied before pistil receptivity (3 weeks before anthesis) and at stem elongation stage 31, 39/60; flowering stage 69; fruit stages 7-75 and continued for a total of five applications at 14-day intervals. We evaluated enzyme activities (SOD, H2O2, CAT and GPx), AC, phenols, flavonoids, leaf area, chlorophyll, total anthocyanins and nut yield and quality (nut weight and % kernel). The mineral concentrations in the leaflets were also determined. The mineral concentrations (N, P, K, Ca, Mg, Fe, Cu, Mn, Ni, Zn and B) in the leaflets were also determined. Spraying ZnO NPs and B increased SOD activity, CA, chlorophyll concentration, mineral nutrients (N, K, Ca, Zn and B) and yield. However, reductions were observed for CAT activity, nut quality and concentrations of phenol, flavonoid, anthocyanin and Fe. Boron increased GPx activity and P concentration. These results demonstrate that spraying low doses (50 mg L-1) of ZnO NPs and B can help reduce oxidative stress and increase yield, nut quality and leaf concentrations of Zn and B in young cv. Wichita pecan trees established on a calcareous soil.

Association between Caregiver-perceived Health Care Provider Cultural Sensitivity and Child Health Status in the National Survey of Children's Health: 2016-2020.

OBJECTIVES: To examine the association between caregiver-perceived cultural sensitivity of health care providers and child health status in the United States. METHODS: We analyzed National Survey of Children's Health data (n = 145,226) from 2016-2020. Using logistic regression, we determined odds of reporting a better health status by level of caregiver-perceived provider cultural sensitivity while controlling for potential confounders. RESULTS: Children with providers perceived as more culturally sensitive by their caregivers had 2.38 times the odds (95% confidence interval: 1.73, 3.28) of enjoying a better caregiver-assessed health status compared with children whose providers were perceived as less culturally sensitive. Caregivers of BIPOC children in our sample were 1.99 times more likely (95% CI: 1.89, 2.10) to report their provider as only sometimes or never culturally sensitive. CONCLUSIONS: Cultural sensitivity of health care providers, as perceived by caregivers, was associated with caregiver-assessed child health status in our study. This association remained significant when controlling for various sociodemographic variables. Our findings highlight the need for more research around the potential positive impact that improving provider cultural sensitivity could have on the health of children who are Black, Indigenous, or other People of Color (BIPOC).

Haemodynamic support with percutaneous devices in patients with cardiogenic shock: the current evidence of mechanical circulatory support.

INTRODUCTION: Cardiogenic shock (CS) is a complex life-threatening condition that results from primary cardiac dysfunction, leading to persistent hypotension and systemic hypoperfusion. Among the therapeutic options for CS are various percutaneous mechanical circulatory support (MCS) devices that have emerged as an increasingly effective hemodynamic support option. Percutaneous therapies can act as short-term mechanical circulatory assistance and can be split into intra-aortic balloon pump (IABP) and non-IABP percutaneous mechanical devices. AREAS COVERED: This review will evaluate the MCS value while considering the mortality rate improvements. We also aim to outline the function of pharmacotherapies and percutaneous hemodynamic MCS devices in managing CS patients to avoid the onset of end-organ dysfunction and improve both early and late outcomes. EXPERT OPINION: Given the complexity, acuity and high mortality associated with CS, and despite the availability and efficacy of pharmacological management, MCS is required to achieve hemodynamic stability and improve survival. Various percutaneous MCS devices are available with varying indications and clinical outcomes. The rates of early mortality and complications were found to be comparable between the four devices, yet, IABP seemed to show the most optimal clinical profile whilst ECMO demonstrated its more long-term efficacy.

Cortical beta oscillations help synchronise muscles during static posture holding in healthy motor control.

How cortical oscillations are involved in the coordination of functionally coupled muscles and how this is modulated by different movement contexts (static vs dynamic) remains unclear. Here, this is investigated by recording high-density electroencephalography (EEG) and electromyography (EMG) from different forearm muscles while healthy participants (n = 20) performed movement tasks (static and dynamic posture holding, and reaching) with their dominant hand. When dynamic perturbation was applied, beta band (15-35 Hz) activities in the motor cortex contralateral to the performing hand reduced during the holding phase, comparative to when there was no perturbation. During static posture holding, transient periods of increased cortical beta oscillations (beta bursts) were associated with greater corticomuscular coherence and increased phase synchrony between muscles (intermuscular coherence) in the beta frequency band compared to the no-burst period. This effect was not present when resisting dynamic perturbation. The results suggest that cortical beta bursts assist synchronisation of different muscles during static posture holding in healthy motor control, contributing to the maintenance and stabilisation of functional muscle groups. Theoretically, increased cortical beta oscillations could lead to exaggerated synchronisation in different muscles making the initialisation of movements more difficult, as observed in Parkinson's disease.

Evidence for direct CO2 -mediated alterations in cerebral oxidative metabolism in humans.

AIM: How the cerebral metabolic rates of oxygen and glucose utilization (CMRO2 and CMRGlc, respectively) are affected by alterations in arterial PCO2 (PaCO2) is equivocal and therefore was the primary question of this study. METHODS: This retrospective analysis involved pooled data from four separate studies, involving 41 healthy adults (35 males/6 females). Participants completed stepwise steady-state alterations in PaCO2 ranging between 30 and 60 mmHg. The CMRO2 and CMRGlc were assessed via the Fick approach (CBF × arterial-internal jugular venous difference of oxygen or glucose content, respectively) utilizing duplex ultrasound of the internal carotid artery and vertebral artery to calculate cerebral blood flow (CBF). RESULTS: The CMRO2 was altered by 0.5 mL × min-1 (95% CI: -0.6 to -0.3) per mmHg change in PaCO2 (p < 0.001) which corresponded to a 9.8% (95% CI: -13.2 to -6.5) change in CMRO2 with a 9 mmHg change in PaCO2 (inclusive of hypo- and hypercapnia). The CMRGlc was reduced by 7.7% (95% CI: -15.4 to -0.08, p = 0.045; i.e., reduction in net glucose uptake) and the oxidative glucose index (ratio of oxygen to glucose uptake) was reduced by 5.6% (95% CI: -11.2 to 0.06, p = 0.049) with a + 9 mmHg increase in PaCO2. CONCLUSION: Collectively, the CMRO2 is altered by approximately 1% per mmHg change in PaCO2. Further, glucose is incompletely oxidized during hypercapnia, indicating reductions in CMRO2 are either met by compensatory increases in nonoxidative glucose metabolism or explained by a reduction in total energy production.

Long-Term Survival and Reintervention Following Thoracic Endovascular Aortic Repair in Blunt Traumatic Thoracic Aortic Injury: A Systematic Review and Meta-Analysis.

BACKGROUND: Blunt thoracic aortic injury (BTAI) represents one of the most devastating scenarios of vascular trauma. Different management strategies are available with varying clinical outcomes. However, thoracic endovascular aortic repair (TEVAR) has become the first-line option for most BTAI patients, mainly owing to its minimally invasive nature, yielding improved immediate results. This meta-analysis aims to investigate mortality, long-term survival, and reintervention following TEVAR in BTAI. MATERIAL AND METHODS: A systematic review conducted a comprehensive literature search on multiple electronic databases using strict search terms. Twenty-seven studies met the set inclusion/exclusion criteria. A proportional meta-analysis of extracted data was conducted using the Comprehensive Meta-Analysis Software, v.4. RESULTS: 1498 BTAI patients who underwent TEVAR were included. Using the SVS grading system, 2.6% of the population had Grade 1 injuries, 13.6% Grade 2, 62.2% Grade 3, 19.6% Grade 4, and 1.9% unspecific. All-cause mortality did not exceed 20% in all studies except one outlier with a 37% mortality rate. Using the random effects model, the pooled estimate of overall mortality was 12% (95% confidence interval [CI], 5.35-8.55%; I2 = 70.6%). This was 91% (95% CI, 88.6-93.2; I2 = 30.2%) at 6 months, 90.1% (95% CI, 86.7-92.3; I2 = 53.6%) at 1 year, 89.2% (95% CI, 85.2-91.8; I2 = 62.3%) at 2 years, and 88.1% (95% CI, 83.3-90.9; I2 = 69.6%) at 5 years. Moreover, the pooled estimate of reintervention was 6.4% (95% CI, 0.1-0.49%; I2 = 81.7%). CONCLUSIONS: Despite the high morbidity and mortality associated with BTAI, TEVAR has proven to be a safe and effective management strategy with favorable long-term survival and minimal need for reintervention. Nevertheless, diagnosis of BTAI requires a high index of suspicion with appropriate grading and prompt transfer to trauma centers with appropriate TEVAR facilities.

A prospective longitudinal study of risk factors for abdominal aortic aneurysm.

The aim of this study was to identify risk factors for abdominal aortic aneurysm (AAA) from the largest Welsh screening cohort to date. Patients were recruited from 1993 (to 2015) as part of the South East Wales AAA screening programme through general practitioners. Demographic data and risk factors were collected by means of a self-report questionnaire. Statistical tests were performed to determine whether associations could be observed between AAA and potential risk factors. Odds ratios (OR) were also calculated for each of the risk factors identified. A total of 6879 patients were included in the study. Two hundred and seventy-five patients (4.0%) presented with AAA, of which 16% were female and 84% were male. Patients with AAA were older than the (no AAA) control group (p < 0.0001). The following risk factors were identified for AAA: family history of AAA (p < 0.0001); history of vascular surgery (p < 0.0001), cerebrovascular accident (p < 0.0001), coronary heart disease (p < 0.0001), diabetes (p < 0.0001), medication (p = 0.0018), claudication (p < 0.0001), smoking history (p = 0.0001) and chronic obstructive pulmonary disorder (p = 0.0007). AAA is associated with classical vascular risk factors, in addition to other less-well-documented risk factors including previous vascular surgery. These findings have practical implications with the potential to improve future clinical screening of patients in order to reduce AAA mortality.

Subthalamic control of impulsive actions: insights from deep brain stimulation in Parkinson's disease.

Control of actions allows adaptive, goal-directed behaviour. The basal ganglia, including the subthalamic nucleus, are thought to play a central role in dynamically controlling actions through recurrent negative feedback loops with the cerebral cortex. Here, we summarize recent translational studies that used deep brain stimulation to record neural activity from and apply electrical stimulation to the subthalamic nucleus in people with Parkinson's disease. These studies have elucidated spatial, spectral and temporal features of the neural mechanisms underlying the controlled delay of actions in cortico-subthalamic networks and demonstrated their causal effects on behaviour in distinct processing windows. While these mechanisms have been conceptualized as control signals for suppressing impulsive response tendencies in conflict tasks and as decision threshold adjustments in value-based and perceptual decisions, we propose a common framework linking decision-making, cognition and movement. Within this framework subthalamic deep brain stimulation can lead to suboptimal choices by reducing the time that patients take for deliberation before committing to an action. However, clinical studies have consistently shown that the occurrence of impulse control disorders is reduced, not increased, after subthalamic deep brain stimulation surgery. This apparent contradiction can be reconciled when recognizing the multifaceted nature of impulsivity, its underlying mechanisms and modulation by treatment. While subthalamic deep brain stimulation renders patients susceptible to making decisions without proper forethought, this can be disentangled from effects related to dopamine comprising sensitivity to benefits vs. costs, reward delay aversion and learning from outcomes. Alterations in these dopamine-mediated mechanisms are thought to underlie the development of impulse control disorders, and can be relatively spared with reduced dopaminergic medication after subthalamic deep brain stimulation. Together, results from studies using deep brain stimulation as an experimental tool have improved our understanding of action control in the human brain and have important implications for treatment of patients with Neurological disorders.

Towards the Optimization of a Photovoltaic/Membrane Distillation System for the Production of Pure Water.

The production of pure water plays a pivotal role in enabling sustainable green hydrogen production through electrolysis. The current industrial approach for generating pure water relies on energy-intensive techniques such as reverse osmosis. This study unveils a straightforward method to produce pure water, employing real-world units derived from previously simulated and developed laboratory devices. This demonstrated system is cost-effective and boasts low energy consumption, utilizing membrane distillation (MD) driven by the waste heat harnessed from photovoltaic (PV) panels. In a previous study, modeling simulations were conducted to optimize the multi-layered MD system, serving as a blueprint for the construction of prototype devices with a suitable selection of materials, enabling the construction of field-testable units. The most efficient PV-MD device, featuring evaporation and condensation zones constructed from steel sheets and polytetrafluoroethylene (PTFE) membranes, is capable of yielding high-purity water with conductivity levels below 145 µS with high flux rates.

The Roles of Impurities and Surface Area on Thermal Stability and Oxidation Resistance of BN Nanoplatelets.

This study considers the influence of purity and surface area on the thermal and oxidation properties of hexagonal boron nitride (h-BN) nanoplatelets, which represent crucial factors in high-temperature oxidizing environments. Three h-BN nanoplatelet-based materials, synthesized with different purity levels and surface areas (~3, ~56, and ~140 m2/g), were compared, including a commercial BN reference. All materials were systematically analyzed by various characterization techniques, including gas pycnometry, scanning electron microscopy, X-ray diffraction, Fourier-transform infrared radiation, X-ray photoelectron spectroscopy, gas sorption analysis, and thermal gravimetric analysis coupled with differential scanning calorimetry. Results indicated that the thermal stability and oxidation resistance of the synthesized materials were improved by up to ~13.5% (or by 120 °C) with an increase in purity. Furthermore, the reference material with its high purity and low surface area (~4 m2/g) showed superior performance, which was attributed to the minimized reactive sites for oxygen diffusion due to lower surface area availability and fewer possible defects, highlighting the critical roles of both sample purity and accessible surface area in h-BN thermo-oxidative stability. These findings highlight the importance of focusing on purity and surface area control in developing BN-based nanomaterials, offering a path to enhance their performance in extreme thermal and oxidative conditions.

Association between psoas major muscle mass and CPET performance and long-term survival following major colorectal surgery: A retrospective cohort study.

OBJECTIVES: To evaluate whether computed tomography (CT)-derived psoas major muscle measurements could predict preoperative cardiopulmonary exercise testing (CPET) performance and long-term mortality in patients undergoing major colorectal surgery and to compare predictive performance of psoas muscle measurements using 2D approach and 3D approach. METHODS: A retrospective cohort study compliant with STROCSS standards was conducted. Consecutive patients undergoing major colorectal surgery between January 2011 and January 2017 following CPET as part of their preoperative assessment were included. Regression analyses were modelled to investigate association between the CT-derived psoas major muscle mass variables [total psoas muscle area (TPMA), total psoas muscle volume (TPMV) and psoas muscle index (PMI)] and CPET performance and mortality (1-year and 5-year). Discriminative performances of the variables were evaluated using Receiver Operating Characteristic (ROC) curve analysis. RESULTS: A total of 457 eligible patients were included. The median TPMA and TPMV were 21 â€‹cm2 (IQR: 15-27) and 274 â€‹cm3 (IQR: 201-362), respectively. The median PMI measured via 2D and 3D approaches were 7 â€‹cm2/m2 (IQR: 6-9) and 99 â€‹cm3/m2 (IQR: 76-120), respectively. The risks of 1-year and 5-year mortality were 7.4% and 27.1%, respectively. Regression analyses showed TPMA, TPMV, and PMI can predict preoperative CPET performance and long-term mortality. However, ROC curve analyses showed no significant difference in predictive performance amongst TPMA, TPMV, and PMI. CONCLUSION: Radiologically-measured psoas muscle mass variables may predict preoperative CPET performance and may be helpful with informing more objective selection of patients for preoperative CPET and prehabilitation.

Subthalamic stimulation modulates context-dependent effects of beta bursts during fine motor control.

Increasing evidence suggests a considerable role of pre-movement beta bursts for motor control and its impairment in Parkinson's disease. However, whether beta bursts occur during precise and prolonged movements and if they affect fine motor control remains unclear. To investigate the role of within-movement beta bursts for fine motor control, we here combine invasive electrophysiological recordings and clinical deep brain stimulation in the subthalamic nucleus in 19 patients with Parkinson's disease performing a context-varying task that comprised template-guided and free spiral drawing. We determined beta bursts in narrow frequency bands around patient-specific peaks and assessed burst amplitude, duration, and their immediate impact on drawing speed. We reveal that beta bursts occur during the execution of drawing movements with reduced duration and amplitude in comparison to rest. Exclusively when drawing freely, they parallel reductions in acceleration. Deep brain stimulation increases the acceleration around beta bursts in addition to a general increase in drawing velocity and improvements of clinical function. These results provide evidence for a diverse and task-specific role of subthalamic beta bursts for fine motor control in Parkinson's disease; suggesting that pathological beta bursts act in a context dependent manner, which can be targeted by clinical deep brain stimulation.

Severe hypoxaemic hypercapnia compounds cerebral oxidative-nitrosative stress during extreme apnoea: Implications for cerebral bioenergetic function.

We examined the extent to which apnoea-induced extremes of oxygen demand/carbon dioxide production impact redox regulation of cerebral bioenergetic function. Ten ultra-elite apnoeists (six men and four women) performed two maximal dry apnoeas preceded by normoxic normoventilation, resulting in severe end-apnoea hypoxaemic hypercapnia, and hyperoxic hyperventilation designed to ablate hypoxaemia, resulting in hyperoxaemic hypercapnia. Transcerebral exchange of ascorbate radicals (by electron paramagnetic resonance spectroscopy) and nitric oxide metabolites (by tri-iodide chemiluminescence) were calculated as the product of global cerebral blood flow (by duplex ultrasound) and radial arterial (a) to internal jugular venous (v) concentration gradients. Apnoea duration increased from 306 ± 62 s during hypoxaemic hypercapnia to 959 ± 201 s in hyperoxaemic hypercapnia (P ≤ 0.001). Apnoea generally increased global cerebral blood flow (all P ≤ 0.001) but was insufficient to prevent a reduction in the cerebral metabolic rates of oxygen and glucose (P = 0.015-0.044). This was associated with a general net cerebral output (v > a) of ascorbate radicals that was greater in hypoxaemic hypercapnia (P = 0.046 vs. hyperoxaemic hypercapnia) and coincided with a selective suppression in plasma nitrite uptake (a > v) and global cerebral blood flow (P = 0.034 to <0.001 vs. hyperoxaemic hypercapnia), implying reduced consumption and delivery of nitric oxide consistent with elevated cerebral oxidative-nitrosative stress. In contrast, we failed to observe equidirectional gradients consistent with S-nitrosohaemoglobin consumption and plasma S-nitrosothiol delivery during apnoea (all P ≥ 0.05). Collectively, these findings highlight a key catalytic role for hypoxaemic hypercapnia in cerebral oxidative-nitrosative stress. KEY POINTS: Local sampling of blood across the cerebral circulation in ultra-elite apnoeists determined the extent to which severe end-apnoea hypoxaemic hypercapnia (prior normoxic normoventilation) and hyperoxaemic hypercapnia (prior hyperoxic hyperventilation) impact free radical-mediated nitric oxide bioavailability and global cerebral bioenergetic function. Apnoea generally increased the net cerebral output of free radicals and suppressed plasma nitrite consumption, thereby reducing delivery of nitric oxide consistent with elevated oxidative-nitrosative stress. The apnoea-induced elevation in global cerebral blood flow was insufficient to prevent a reduction in the cerebral metabolic rates of oxygen and glucose. Cerebral oxidative-nitrosative stress was greater during hypoxaemic hypercapnia compared with hyperoxaemic hypercapnia and coincided with a lower apnoea-induced elevation in global cerebral blood flow, highlighting a key catalytic role for hypoxaemia. This applied model of voluntary human asphyxia might have broader implications for the management and treatment of neurological diseases characterized by extremes of oxygen demand and carbon dioxide production.

Cognition is selectively impaired in males with spinal pain: A retrospective analysis of data from the Longitudinal Study of Ageing Danish Twins.

Cognitive decline and spinal pain (back pain [BP] and neck pain [NP]) represent a major public health challenge, yet the potential relationship between them remains elusive. A retrospective analysis of the Longitudinal Study of Ageing Danish Twins was performed to determine any potential relationships between BP/NP and cognitive function adjusting for age, sex, educational and socioeconomic status. A total of 4731 adults (2788 females/1943 males) aged 78 ± 6 (SD) years were included in the analysis. We observed a 1-month prevalence of 25% with BP, 21% with NP and 11% for combined BP/NP. While there were no differences in cognition scores for males and females reporting combined BP/NP, compared to those without combined BP/NP (34.38 points [95% confidence interval (CI) = 31.88, 36.88] vs. 35.72 points [95% CI = 35.19, 36.26]; P = 0.180; and 35.72 points [95% CI = 35.19, 36.26] vs. 35.85 points [95% CI = 35.39, 36.31]; P = 0.327; for male and females, respectively), an adjusted analysis revealed that males with combined BP/NP presented with lower cognitive scores compared to males without combined BP/NP (81.26 points [95% CI = 73.80, 88.72] vs. 79.48 points [95% CI = 70.31, 88.66]; P = 0.043). The findings of this hypothesis-generating study may highlight a potential sex-specific association between spinal pain and later-life neurodegeneration.

Neuroscience: Therapy modulates decision-making in Parkinson's disease.

There is mounting evidence that decision-making can be affected by treatment in Parkinson's disease. A new study shows that dopamine and deep brain stimulation, two mainstay treatments of Parkinson's, differently affect how patients make decisions weighing rewards against effort costs.