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Search Results: 1 - 10 of 462097 matches for " Maarten A. Hogervorst "
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A new paradigm to induce mental stress: the Sing-a-Song Stress Test (SSST)
Anne-Marie Brouwer,Maarten A. Hogervorst
Frontiers in Neuroscience , 2014, DOI: 10.3389/fnins.2014.00224
Abstract: We here introduce a new experimental paradigm to induce mental stress in a quick and easy way while adhering to ethical standards and controlling for potential confounds resulting from sensory input and body movements. In our Sing-a-Song Stress Test, participants are presented with neutral messages on a screen, interleaved with 1-min time intervals. The final message is that the participant should sing a song aloud after the interval has elapsed. Participants sit still during the whole procedure. We found that heart rate and skin conductance during the 1-min intervals following the sing-a-song stress message are substantially higher than during intervals following neutral messages. The order of magnitude of the rise is comparable to that achieved by the Trier Social Stress Test. Skin conductance increase correlates positively with experienced stress level as reported by participants. We also simulated stress detection in real time. When using both skin conductance and heart rate, stress is detected for 18 out of 20 participants, approximately 10 s after onset of the sing-a-song message. In conclusion, the Sing-a-Song Stress Test provides a quick, easy, controlled and potent way to induce mental stress and could be helpful in studies ranging from examining physiological effects of mental stress to evaluating interventions to reduce stress.
A method to assess the clinical significance of unclassified variants in the BRCA1 and BRCA2 genes based on cancer family history
Encarna B Gómez García, Jan C Oosterwijk, Maarten Timmermans, Christi J van Asperen, Frans BL Hogervorst, Nicoline Hoogerbrugge, Rogier Oldenburg, Senno Verhoef, Charlotte J Dommering, Margreet GEM Ausems, Theo AM van Os, Annemarie H van der Hout, Marjolijn Ligtenberg, Ans van den Ouweland, Rob B van der Luijt, Juul T Wijnen, Jan JP Gille, Patrick J Lindsey, Peter Devilee, Marinus J Blok, Maaike PG Vreeswijk
Breast Cancer Research , 2009, DOI: 10.1186/bcr2223
Abstract: We developed logistic regression models with the best combination of clinical features that distinguished a positive control of BRCA pathogenic variants (115 families) from a negative control population of BRCA variants initially classified as UVs and later considered neutral (38 families).The models included a combination of BRCAPRO scores, Myriad scores, number of ovarian cancers in the family, the age at diagnosis, and the number of persons with ovarian tumors and/or breast tumors. The areas under the receiver operating characteristic curves were respectively 0.935 and 0.836 for the BRCA1 and BRCA2 models. For each model, the minimum receiver operating characteristic distance (respectively 90% and 78% specificity for BRCA1 and BRCA2) was chosen as the cutoff value to predict which UVs are deleterious from a study population of 12 UVs, present in 59 Dutch families. The p.S1655F, p.R1699W, and p.R1699Q variants in BRCA1 and the p.Y2660D, p.R2784Q, and p.R3052W variants in BRCA2 are classified as deleterious according to our models. The predictions of the p.L246V variant in BRCA1 and of the p.Y42C, p.E462G, p.R2888C, and p.R3052Q variants in BRCA2 are in agreement with published information of them being neutral. The p.R2784W variant in BRCA2 remains uncertain.The present study shows that these developed models are useful to classify UVs in clinical genetic practice.Cancer risk counseling of patients and families with an unclassified variant of the breast cancer (BC) genes BRCA1 and/or BRCA2 (MIM numbers 113705 and 600185, respectively) has become a prominent issue for genetic counselors and oncologists. About one-third of the genetic variants in BRCA1 and 50% of those found in BRCA2 reported by the Breast Cancer Information Core [1] are considered genetic variants of unknown clinical significance, also known as unclassified variants (UVs), because of the uncertainty about their cancer risks. This is often the case for missense variations or when the nucleotide chan
Roel Hijink, Voormalige concentratiekampen. De monumentalisering van Duitse kampen in Nederland
Susan Hogervorst
BMGN : Low Countries Historical Review , 2013,
A Degenerate Bose-Fermi Mixture of Metastable Atoms
J. M. McNamara,T. Jeltes,A. S. Tychkov,W. Hogervorst,W. Vassen
Physics , 2006, DOI: 10.1103/PhysRevLett.97.080404
Abstract: We report the observation of simultaneous quantum degeneracy in a dilute gaseous Bose-Fermi mixture of metastable atoms. Sympathetic cooling of helium-3 (fermion) by helium-4 (boson), both in the lowest triplet state, allows us to produce ensembles containing more than 10^6 atoms of each isotope at temperatures below 1 micro-Kelvin, and achieve a fermionic degeneracy parameter of T/Tf=0.45. Due to their high internal energy, the detection of individual metastable atoms with sub-nanosecond time resolution is possible, permitting the study of bosonic and fermionic quantum gases with unprecedented precision. This may lead to metastable helium becoming the mainstay of quantum atom optics.
Atom lithography with two-dimensional optical masks
S. J. H. Petra,K. A. H. van Leeuwen,L. Feenstra,W. Hogervorst,W. Vassen
Physics , 2004, DOI: 10.1007/s00340-004-1569-4
Abstract: With a two-dimensional (2D) optical mask, nanoscale patterns are created for the first time in an atom lithography process using metastable helium atoms. The internal energy of the atoms is used to locally damage a hydrofobic resist layer, which is removed in a wet etching process. Experiments have been performed with several polarizations for the optical mask, resulting in different intensity patterns, and corresponding nanoscale structures. The results for a linear polarized light field show an array of holes with a diameter of 260 nm, in agreement with a computed pattern. With a circularly polarized light field a line pattern is observed with a spacing of 766 nm. Simulations taking into account many possible experimental imperfections can not explain this pattern.
Numerical simulations on the motion of atoms travelling through a standing-wave light field
S. J. H. Petra,K. A. H. van Leeuwen,L. Feenstra,W. Hogervorst,W. Vassen
Physics , 2003, DOI: 10.1140/epjd/e2003-00229-y
Abstract: The motion of metastable helium atoms travelling through a standing light wave is investigated with a semi-classical numerical model. The results of a calculation including the velocity dependence of the dipole force are compared with those of the commonly used approach, which assumes a conservative dipole force. The comparison is made for two atom guiding regimes that can be used for the production of nanostructure arrays; a low power regime, where the atoms are focused in a standing wave by the dipole force, and a higher power regime, in which the atoms channel along the potential minima of the light field. In the low power regime the differences between the two models are negligible and both models show that, for lithography purposes, pattern widths of 150 nm can be achieved. In the high power channelling regime the conservative force model, predicting 100 nm features, is shown to break down. The model that incorporates velocity dependence, resulting in a structure size of 40 nm, remains valid, as demonstrated by a comparison with quantum Monte-Carlo wavefunction calculations.
Complexity on dwarf galaxies scale: A bimodal distribution function in Sculptor
Maarten A. Breddels,Amina Helmi
Physics , 2014, DOI: 10.1088/2041-8205/791/1/L3
Abstract: In previous work we have presented Schwarzschild models of the Sculptor dSph, demonstrating that this system could be embedded in dark matter halos that are either cusped or cored. Here we show that the non-parametric distribution function recovered through Schwarschild's method is bimodal in energy and angular momentum space for all best fitting mass models explored. We demonstrate that this bimodality is directly related to the two components known to be present in Sculptor through stellar populations analysis, although our method is purely dynamical in nature and does not use this prior information. It therefore constitutes independent confirmation of the existence of two physically distinct dynamical components in Sculptor and suggests a rather complex assembly history for this dwarf galaxy.
An analytic distribution function for a massless cored stellar system in a cuspy dark matter halo
Maarten A. Breddels,Amina Helmi
Physics , 2013, DOI: 10.1051/0004-6361/201322449
Abstract: We demonstrate the existence of distribution functions that can be used to represent spherical massless cored stellar systems embedded in cuspy dark matter halos with constant mildly tangential velocity anisotropy. In particular, we derive analytically the functional form of the distribution function for a Plummer stellar sphere in a Hernquist dark halo, for \beta_0 = -0.5 and for different degrees of embedding. This particular example satisfies the condition that the central logarithmic slope of the light profile \gamma_0 > 2 \beta_0. Our models have velocity dispersion profiles similar to those observed in nearby dwarf spheroidal galaxies. Hence they can be used to generate initial conditions for a variety of problems, including N-body simulations that may represent dwarf galaxies in the Local Group.
Finite size scaling and triviality of φ^4 theory on an antiperiodic torus
Matthijs Hogervorst,Ulli Wolff
Physics , 2011, DOI: 10.1016/j.nuclphysb.2011.10.028
Abstract: Worm methods to simulate the Ising model in the Aizenman random current representation including a low noise estimator for the connected four point function are extended to allow for antiperiodic boundary conditions. In this setup several finite size renormalization schemes are formulated and studied with regard to the triviality of \phi^4 theory in four dimensions. With antiperiodicity eliminating the zero momentum Fourier mode a closer agreement with perturbation theory is found compared to the periodic torus.
A Large Atom Number Metastable Helium Bose-Einstein Condensate
A. S. Tychkov,T. Jeltes,J. M. McNamara,P. J. J. Tol,N. Herschbach,W. Hogervorst,W. Vassen
Physics , 2005, DOI: 10.1103/PhysRevA.73.031603
Abstract: We have produced a Bose-Einstein condensate of metastable helium (4He*) containing over 1.5x10^7 atoms, which is a factor of 25 higher than previously achieved. The improved starting conditions for evaporative cooling are obtained by applying one-dimensional Doppler cooling inside a magnetic trap. The same technique is successfully used to cool the spin-polarized fermionic isotope (3He*), for which thermalizing collisions are highly suppressed. Our detection techniques include absorption imaging, time-of-flight measurements on a microchannel plate detector and ion counting to monitor the formation and decay of the condensate.
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