We develop a theory that explains the origin of the high force sensitivity observed in multifrequency force microscopy experiments. The ability of the microscope to extract complementary information ...on the surface properties is increased by the simultaneous excitation of several flexural cantilever modes. The force sensitivity in multifrequency operation is about 0.2 pN. The analytical model identifies the virial and the energy dissipated by the tip-surface forces as the parameters responsible for the material contrast. The agreement obtained among the theory, experiments and numerical simulations validates the model.
Cocaine/crack abstinence periods have higher risk of relapse. Abstinence as initial part of the recovery process is affected by learning and memory changes that could preserve the addictive cycle. To ...further understand how the interruption of cocaine/crack consumption affects neurotrophin level we performed the present systematic review and meta-analysis following the PRISMA statement (number CRD42019121643). The search formula was conducted in PubMed, Web of Science, Embase, ScienceDirect, and Google Scholar databases. The inclusion criterion was cocaine use disorder in 18 to 60-year-old people, measuring at least one neurotrophin in blood before and after a controlled abstinence period. Studies without pre-post design were excluded. Five investigations had nine different reports, four of them were subjected to a meta-analysis (n = 146). GRADE risk of bias method was followed. Individual studies reported increased peripheral brain derived neurotrophic factor (BDNF) after abstinence, evidence pooled by Hedge's g showed no significant change in BDNF after abstinence. Relevant heterogeneity in the length of the abstinence period (12-32 days), last cocaine/crack consumption monitoring and blood processing were detected that could help to explain non-significant results. Further improved methods are suggested, and a potential BDNF augmentation hypothesis is proposed that, if true, would help to understand initial abstinence as a re-adaptation period influenced by neurotrophins such as the BDNF.
In this paper, we present a controller design and its implementation on a mini rotorcraft having four rotors. The dynamic model of the four-rotor rotorcraft is obtained via a Lagrange approach. The ...proposed controller is based on Lyapunov analysis using a nested saturation algorithm. The global stability analysis of the closed-loop system is presented. Real-time experiments show that the controller is able to perform autonomously the tasks of taking off, hovering, and landing.
A recent stable isotope analysis of striped dolphins Stenella coeruleoalba stranded along the Spanish Mediterranean coast suggested a shift from a diet dominated by sardine Sardina pilchardus in 1990 ...towards a diet dominated by juvenile hake Merluccius merluccius in 2007–2008. This shift, apparently related to trophic cascade effects caused by overfishing, could entail long-term problems for the energetic balance of dolphins. In this study, we re-examined these conclusions using stomach content analysis of 140 striped dolphins stranded in the same area during the period 1990–2012. Remains of 13 769 individual preys of 37 fish and 24 cephalopod taxa were detected. Oceanic and neritic prey were regularly found throughout the whole period; however, in the last decade, there was a strong relative decrease of oceanic cephalopods and a significant increase of 2 lower-shelf prey, i.e. juvenile hake and southern shortfin squid Illex coindetii, which together accounted for over 50% of the index of relative importance. Sardine was found only in 1 and 10% of dolphins in the 1990s and 2000s, respectively. Surveys in the study area indicate that striped dolphins favour waters 900 to 1900 m in depth, which suggests that dolphins increased predatory incursions into neritic waters in the 2000s. This habitat shift was most likely related to an increase of some neritic prey, especially juvenile hake which, according to trophodynamic models, was linked to the decline of demersal top predators. At present, stomach contents and demographic data do not support a putative impact of overfishing on the striped dolphin population.
This article presents a comparison of three control techniques: nested saturations, backstepping, and sliding modes. The control objective consists of obtaining the best control strategy to stabilize ...the position of a quad-rotor unmanned aerial vehicle (UAV) when using visual feedback. We propose a vision-based method to measure translational speed as well as the UAV 3D position in a local frame. The three selected controllers were implemented and tested in real-time experiments. The obtained results demonstrate the performance of such methodologies applied to the quad-rotor system.
In this paper, an optimal bounded robust control algorithm for secure autonomous navigation in quadcopter vehicles is proposed. The controller is developed combining two parts; one dedicated to ...stabilize the closed-loop system and the second one for dealing and estimating external disturbances as well unknown nonlinearities inherent to the real system’s operations. For bounding the energy used by the system during a mission and, without losing its robustness properties, the quadratic problem formulation is used considering the actuators system constraints. The resulting optimal bounded control scheme improves considerably the stability and robustness of the closed-loop system and at the same time bounds the motor control inputs. The controller is validated in real-time flights and in unconventional conditions for high wind-gusts and Loss of Effectiveness in two rotors. The experimental results demonstrate the good performance of the proposed controller in both scenarios.
Current treatments for Alzheimer's disease (AD) have a limited clinical response and methods, such as repetitive transcranial magnetic stimulation (rTMS), are being studied as possible treatments for ...the clinical symptoms with positive results. However, there is still seldom information on the type of rTMS protocols that deliver the best clinical improvement in AD. Objetive: To compare the clinical response between a simple stimulation protocol on the left dorsolateral prefrontal cortex (lDLPFC) against a complex protocol using six regions of interest. Methods: 19 participants were randomized to receive any of the protocols. The analysis of repeated measures evaluated the change.
Both protocols were equally proficient at improving cognitive function, behavior and functionality after 3 weeks of treatment, and the effects were maintained for 4 weeks more without treatment.
We suggest rTMS on the lDLPFC could be enough to provide a clinical response, and the underlying mechanisms should be studied.
This study describes a technique to estimate green area index (GAI) of row crops from gap fraction measurements at 57.5° perpendicular to the row using downward looking digital photos. This ...particular directional configuration makes the gap fraction independent from leaf angle distribution and minimizes leaf clumping when plants overlap within the row and when rows overlap from this particular direction which is the case for several crops including wheat, maize, sorghum, sunflower and soybean. This was demonstrated from generic row crop canopy architecture models. Additional simulations over realistic 3D scenes of wheat crop allowed to calibrate the following equation relating the gap fraction (
Po(57.5°)) to GAI for this particular directional configuration:
Po(57.5°)
=
e
−0.824·
GAI
. This relationship appears very robust across development stages, cultivars and variations due to environmental conditions. When comparing with the situation where leaves are randomly distributed, performances degrade significantly, demonstrating that some residual clumping (
Ω
=
0.89) has to be accounted for.
Field experiments were conducted over wheat crops using colour digital photos taken at 57.5° zenith angle from above in a compass direction perpendicular to the rows. The corresponding gap fraction was computed after image segmentation based on the three colours. The equation derived from wheat architecture model simulations was then used to estimate GAI. Comparison with destructive GAI field measurements shows very good performances with a relative RMSE of 12%.
GAI values estimated with this technique were also showing a good consistency with LAI2000
PAI (plant area index) estimates. However, systematic biases between the two estimates were observed, due to canopy elements at the bottom of the canopy not sampled by the instrument because of the height of the LAI2000 sensor, as well as accounting for the residual clumping in the proposed method.
These results suggest that this
GAI estimation method is very efficient over wheat crops from emergence up to flowering independently from possible architecture variation due to genotype or environmental condition differences. Possible extension to other crops is discussed.
PDF
