Populations in previously glaciated regions are often genetically depauperate in comparison with populations at lower latitudes, due either to bottlenecks experienced in post-glacial colonization or ...to contemporary genetic drift in small, peripheral populations. Populations of the rare self-fertilizing North American orchid Isotria medeoloides are largest in the previously glaciated region near the northern range limit, allowing us to examine the role of historical versus contemporary processes in determining population genetic diversity and structure. If contemporary processes predominate, genetic diversity should increase with increasing census size. In contrast, if sequential bottlenecks associated with colonization are paramount, diversity should decrease with latitude and be relatively insensitive to census size. We genotyped 299 individuals from 20 populations at four variable microsatellite loci to contrast genetic diversity and structure for populations in previously glaciated regions versus previously unglaciated regions. Populations were highly inbred (F=0.95) and highly differentiated (R(ST)=0.485). Across all sampled populations, genetic diversity decreased and genetic differentiation increased with declining population size. Small southern populations were especially differentiated and genetically depauperate. In the glaciated part of the range, genetic diversity increased as populations approached the northern range limit, demonstrating the centrality of contemporary processes for this post-glacial colonist.
The DELPHI pixels Becks, K.H.; Borghi, P.; Brunet, J.M. ...
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment,
02/1997, Letnik:
386, Številka:
1
Journal Article, Conference Proceeding
Recenzirano
To improve tracking in the very forward direction for running at LEP200, the angular acceptance of the DELPHI Vertex detector has been extended from 45° to 11° with respect to the beam axis. Pixel ...detector crowns cover the region between 25° and 13°. Due to very tight space and material thickness constraints it was necessary to develop new techniques (integrated busses in the detector substrate, high density layout on Kapton, etc.). About 1000 cm
2 of pixels are already installed and working in DELPHI. Techniques, tests and production of these detectors will be described, as well as the main problems encountered during this work.
•Finite element modeling of ultrasound propagation in aluminum foams was performed.•The models included microstructures of water-saturated aluminum foams.•Ultrasonic attenuation and velocity in ...aluminum foams were simulated.•To verify the simulation results, corresponding experiments were performed.•The simulated parameters were in good agreement with the experimental results.
The present study investigated the accuracy of micro-scale finite element modeling for simulating broadband ultrasound propagation in water-saturated trabecular bone-mimicking phantoms. To this end, five commercially manufactured aluminum foam samples as trabecular bone-mimicking phantoms were utilized for ultrasonic immersion through-transmission experiments. Based on micro-computed tomography images of the same physical samples, three-dimensional high-resolution computational samples were generated to be implemented in the micro-scale finite element models. The finite element models employed the standard Galerkin finite element method (FEM) in time domain to simulate the ultrasonic experiments. The numerical simulations did not include energy dissipative mechanisms of ultrasonic attenuation; however, they expectedly simulated reflection, refraction, scattering, and wave mode conversion. The accuracy of the finite element simulations were evaluated by comparing the simulated ultrasonic attenuation and velocity with the experimental data. The maximum and the average relative errors between the experimental and simulated attenuation coefficients in the frequency range of 0.6−1.4MHz were 17% and 6% respectively. Moreover, the simulations closely predicted the time-of-flight based velocities and the phase velocities of ultrasound with maximum relative errors of 20m/s and 11m/s respectively. The results of this study strongly suggest that micro-scale finite element modeling can effectively simulate broadband ultrasound propagation in water-saturated trabecular bone-mimicking structures.
Commissioning of the DELPHI Pixel Detector Becks, K.H; Brunet, J.M; Caccia, M ...
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment,
1998, Letnik:
418, Številka:
1
Journal Article, Conference Proceeding
Recenzirano
The DELPHI Vertex Detector has been upgraded for LEP200 with 2 layers of pixel detectors and 2 layers of ministrips as endcaps, thus covering the polar angular range between 10° and 21° and allowing ...for standalone pattern recognition. During the 1995/96 shutdown the first 95 modules were installed and the installation was completed in May 97 with all 152 modules. Production yields and failures during the assembly will be presented. The detector operated at a threshold of around 9000 electrons resulting in a number of noisy pixels at the 10
−3 level. After masking these hot pixels in the readout, the remaining number of random hits per event is at the 10
−6 level. The observed resolution of about 100
μm is close to the expectation for binary readout. The track reconstruction efficiency increased by more than 100% in the central part of the forward tracker.
Progress in the construction of the DELPHI pixel detector Becks, K.H.; Borghi, P.; Caccia, M. ...
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment,
08/1997, Letnik:
395, Številka:
3
Journal Article, Conference Proceeding
Recenzirano
The status of the pixel detector for the DELPHI Silicon Tracker is presented. The main characteristics of the detector, the readout chip and the assembly are summarized.
First results from the DELPHI pixel detector Becks, K.H.; Brunet, J.M.; Caccia, M. ...
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment,
05/1998, Letnik:
409, Številka:
1-3
Journal Article, Conference Proceeding
Recenzirano
In 1996 the DELPHI experiment at LEP has upgraded its silicon tracker. In the forward region, pixel detectors were installed. The pixel commissioning and the first results are reported.
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