We demonstrate that a rotating magnetic field can be used to apply a controlled torque on superparamagnetic beads which leads to a tunable bead rotation frequency in fluid. Smooth rotation is ...obtained for field rotation frequencies many orders of magnitude higher than the bead rotation frequency. A quantitative model is developed, based on results from a comprehensive set of experiments at different field strengths and frequencies. At low frequencies (<10Hz), rotation is due to a small permanent magnetic moment in the bead. At high frequencies (kHz–MHz), the torque results from a phase lag between the applied field and the induced magnetic moment, caused by the non-zero relaxation time of magnetic nanoparticles in the bead. The control of torque and rotation will enable novel functional assays in bead-based biosensors.
We demonstrate the real-time on-chip detection and manipulation of single 1
μm superparamagnetic particles in solution, with the aim to develop a biosensor that can give information on biological ...function. Our chip-based sensor consists of micro-fabricated current wires and giant magneto resistance (GMR) sensors. The current wires serve to apply force on the particles as well as to magnetize the particles for on-chip detection. The sensitivity profile of the sensor was reconstructed by simultaneously measuring the sensor signal and the position of an individual particle crossing the sensor. A single-dipole model reproduces the measured sensitivity curve for a 1
μm bead. For a 2.8
μm bead the model shows deviations, which we attribute to the fact that the particle size becomes comparable to the sensor width. In the range between 1 and 10 particles, we observed a linear relationship between the number of beads and the sensor signal. The real-time detection and manipulation of individual particles opens the possibility to perform on-chip high-parallel single-particle assays.
Sedentary time (ST) has been reported to have a range of negative health effects in adults, however, the evidence for such effects among children and adolescents is sparse. The primary aim of the ...study was to examine associations between changes in sedentary behavior (time and fragmentation) and changes in adiposity across childhood and adolescence.
Participants were recruited as part of the Gateshead Millennium Study. Measures were taken at age 7 (n=502), 9 (n=506), 12 (n=420) and 15 years (n=306). Participants wore an ActiGraph GT1M and accelerometer epochs were 'sedentary' when recorded counts were ⩽25 counts per 15 s. ST was calculated and fragmentation (SF) was assessed by calculating the number of sedentary bouts per sedentary hour. Associations of changes in ST and SF with changes in adiposity (body mass index (BMI), and fat mass index (FMI)) were examined using bivariate linear spline models.
Increasing ST by 1% per year was associated with an increase in BMI of 0.08 kg m
per year (95% CI: 0.06-0.10; P<0.001) and FMI of 0.15 kg m
per year (0.11-0.19; P<0.001). Change in SF was associated with BMI and FMI (P<0.001). An increase of 1 bout per sedentary hour per year (that is, sedentary time becoming more fragmented) was associated with an increase in BMI of 0.07 kg m
per year (0.06-0.09; P<0.001) and an increase in FMI of 0.14 kg m
per year (0.10-0.18; P<0.001) over the 8 years period. However, an increase in SF between 9-12 years was associated with a 0.09 kg m
per year decrease in BMI (-0.18-0.00; P=0.046) and 0.11 kg m
per year decrease in FMI (-0.22-0.00; P=0.049).
Increased ST and increased SF from 7-15 years were associated with increased adiposity. This is the first study to show age-specific associations between change in objectively measured sedentary behavior and adiposity after adjustment of moderate-to-vigorous-intensity physical activity in children and adolescents. The study suggests that, targeting sedentary behavior for obesity prevention may be most effective during periods in which we see large increases in ST.
There is a plethora of cross-sectional work on maternal perceptions of child weight status showing that mothers typically do not classify their overweight child as being overweight according to ...commonly used clinical criteria. Awareness of overweight in their child is regarded as an important prerequisite for mothers to initiate appropriate action. The gap in the literature is determining whether, if mothers do classify their overweight child's weight status correctly, this is associated with a positive outcome for the child's body mass index (BMI) at a later stage.
To explore longitudinal perceptions of child weight status from mothers of a contemporary population-based birth cohort (Gateshead Millennium Study) and relationships of these perceptions with future child weight gain.
Data collected in the same cohort at 7, 12 and 15 years of age: mothers' responses to two items concerning their child's body size; child's and mother's BMI; pubertal maturation; demographic information.
Mothers' perceptions of whether their child was overweight did not change markedly over time. Child BMI was the only significant predictor of mothers' classification of overweight status, and it was only at the extreme end of the overweight range and in the obese range that mothers reliably described their child as overweight. Even when mothers did appropriately classify their child as overweight at an earlier stage, this was not related to relatively lower child BMI a few years later.
Mothers tend to classify their child as overweight in only more extreme cases. It is an important finding that no beneficial impact was shown on later child BMI in overweight children whose mothers classified their child's weight status as overweight at an earlier stage.
The SoLid collaboration has developed a new detector technology to detect electron anti-neutrinos at close proximity to the Belgian BR2 reactor at surface level. A 288kg prototype detector was ...deployed in 2015 and collected data during the operational period of the reactor and during reactor shut-down. Dedicated calibration campaigns were also performed with gamma and neutron sources. This paper describes the construction of the prototype detector with a high control on its proton content and the stability of its operation over a period of several months after deployment at the BR2 reactor site. All detector cells provide sufficient light yields to achieve a target energy resolution of better than 20%/ E(MeV). The capability of the detector to track muons is exploited to equalize the light response of a large number of channels to a precision of 3% and to demonstrate the stability of the energy scale over time. Particle identification based on pulse-shape discrimination is demonstrated with calibration sources. Despite a lower neutron detection efficiency due to triggering constraints, the main backgrounds at the reactor site were determined and taken into account in the shielding strategy for the main experiment. The results obtained with this prototype proved essential in the design optimization of the final detector.
We demonstrate the ability to measure torsion stiffness of a protein complex by applying a controlled torque on a magnetic particle. As a model system we use protein G bound to an IgG antibody. The ...protein pair is held between a magnetic particle and a polystyrene substrate. The angular orientation of the magnetic particle shows an oscillating behavior upon application of a rotating magnetic field. The amplitude of the oscillation increases with a decreasing surface coverage of antibodies on the substrate and with an increasing magnitude of the applied field. For decreasing antibody coverage, the torsion spring constant converges to a minimum value of 1.5 × 10
3 pN·nm/rad that corresponds to a torsion modulus of 4.5 × 10
4 pN·nm
2. This torsion stiffness is an upper limit for the molecular bond between the particle and the surface that is tentatively assigned to a single protein G–IgG protein pair. This assignment is supported by interpreting the measured stiffness with a simple mechanical model that predicts a two orders of magnitude larger stiffness for the protein G–IgG complex than values found for micrometer length dsDNA. This we understand from the structural properties of the molecules, i.e
., DNA is a long and flexible chain-like molecule, whereas the antibody-antigen couple is orders of magnitude smaller and more globular in shape due to the folding of the molecules.
The H1 very forward proton spectrometer at HERA Astvatsatourov, A.; Cerny, K.; Delvax, J. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2014, Letnik:
736
Journal Article
Recenzirano
The very forward proton spectrometer, VFPS, is a component of the H1 detector at the HERA collider. Scattered protons emitted with a polar angle less than 1mrad and carrying a fractional energy 1−xP, ...0.008<xP≤0.028 of the incident proton beam energy can be detected by scintillating fiber detectors which are read out by position sensitive photo-multipliers. These detectors are contained in Roman pot stations which are moved close to the circulating proton beam. The structure, operation and performance of the two Roman pot stations located at about 220m from the H1 interaction point in the cryogenic section of the proton ring are described.
. The interactions between particles and a glass surface are measured using a new technique based on measuring the rotational behavior of individual magnetic particles upon excitation with rotating ...magnetic fields.
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▶ We developed a new technique to probe interactions between particles and substrates. ▶ We measured the field-induced rotation of many magnetic particles in parallel. ▶ The interaction between streptavidin-coated particles and glass is measured. ▶ Binding between particles and glass is highly dependent on buffer conditions. ▶ Binding increases with increasing ionic strength and decreasing pH.
We demonstrate a new probing technique to measure physicochemical interactions between particles and a substrate in a fluid. The technique is based on the measurement of field-induced rotation of individual magnetic particles in contact with the substrate. The parallel measurement of many particles with single-particle resolution gives reliable statistics in a short time. Using this technique, the interaction between streptavidin-coated magnetic particles and a glass substrate is measured for various buffer conditions. Increased binding is quantified for increasing ionic strength and decreasing pH. The results are found to be in agreement with calculations of electrostatic interactions. We also apply the technique to study how binding is reduced by blocking the substrate with albumin.
Introduction: Excessive time spent sitting, independent of the amount of moderate- to vigorous-intensity physical activity (MVPA) undertaken, is negatively associated with measures of adiposity, ...cardio-metabolic health, and psychosocial health in adults and adolescents. The purpose of this study was to describe sitting time during childcare in children aged 1-5 years,...
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