Characterization of the fundamental properties of wireless CSMA multi-hop networks

A wireless multi-hop network consists of a group of decentralized and self-organized wireless devices that collaborate to complete their tasks in a distributed way. Data packets are forwarded collaboratively hop-by-hop from source nodes to their respective destination nodes with other nodes acting as intermediate relays. Existing and future applications in wireless multi-hop networks will greatly benefit from better understanding of the fundamental properties of such networks. In this thesis we explore two fundamental properties of distributed wireless CSMA multi-hop networks, connectivity and capacity. A network is connected if and only if there is at least one (multi-hop) path between any pair of nodes. We investigate the critical transmission power for asymptotic connectivity in large wireless CSMA multi-hop networks under the SINR model. The critical transmission power is the minimum transmission power each node needs to transmit to guarantee that the resulting network is connected aas. Both upper bound and lower bound of the critical transmission power are obtained analytically. The two bounds are tight and differ by a constant factor only. Next we shift focus to the capacity property. First, we develop a distributed routing algorithm where each node makes routing decisions based on local information only. This is compatible with the distributed nature of large wireless CSMA multi-hop networks. Second, we show that by carefully choosing controllable parameters of the CSMA protocols, together with the routing algorithm, a distributed CSMA network can achieve the order-optimal throughput scaling law. Scaling laws are only up to order and most network design choices have a significant effect on the constants preceding the order while not affecting the scaling law. Therefore we further to analyze the pre-constant by giving an upper and a lower bound of throughput. The tightness of the bounds is validated using simulations

On the Role of Penning Ionization in Photoassociation Spectroscopy

We study the role of Penning ionization on the photoassociation spectra of He(^3S)-He(^3S). The experimental setup is discussed and experimental results for different intensities of the probe laser are shown. For modelling the experimental results we consider coupled-channel calculations of the crossing of the ground state with the excited state at the Condon point. The coupled-channel calculations are first applied to model systems, where we consider two coupled channels without ionization, two coupled channels with ionization, and three coupled channels, for which only one of the excited states is ionizing. Finally, coupled-channel calculations are applied to photoassociation of He(^3S)-He(^3S) and good agreement is obtained between the model and the experimental results.Comment: 14 pages, 18 figures, submitted to the special issue on Cold Molecules of J. Phys.

67 GHz uni-traveling carrier photodetector on an InP-membrane-on-silicon platform

An InP membrane-based uni-traveiling carrier photodetector, heterogeneously integrated on silicon, is realized using double-sided processing. A responsivity of 0.7 A/W at 1.55 mu m and a 3 dB bandwidth beyond 67 GHz are demonstrated

Ionospheric Calibration of Low Frequency Radio Interferometric Observations using the Peeling Scheme: I. Method Description and First Results

Calibration of radio interferometric observations becomes increasingly difficult towards lower frequencies. Below ~300 MHz, spatially variant refractions and propagation delays of radio waves traveling through the ionosphere cause phase rotations that can vary significantly with time, viewing direction and antenna location. In this article we present a description and first results of SPAM (Source Peeling and Atmospheric Modeling), a new calibration method that attempts to iteratively solve and correct for ionospheric phase errors. To model the ionosphere, we construct a time-variant, 2-dimensional phase screen at fixed height above the Earth's surface. Spatial variations are described by a truncated set of discrete Karhunen-Loeve base functions, optimized for an assumed power-law spectral density of free electrons density fluctuations, and a given configuration of calibrator sources and antenna locations. The model is constrained using antenna-based gain phases from individual self-calibrations on the available bright sources in the field-of-view. Application of SPAM on three test cases, a simulated visibility data set and two selected 74 MHz VLA data sets, yields significant improvements in image background noise (5-75 percent reduction) and source peak fluxes (up to 25 percent increase) as compared to the existing self-calibration and field-based calibration methods, which indicates a significant improvement in ionospheric phase calibration accuracy.Comment: 23 pages, 14 figures, 2 tables. Accepted for publication in A&A. Changes in v2: Corrected minor error in Equations A.3 and A.12. Extended acknowledgment

Indium phosphide photonic circuits on silicon electronics

The intimate integration of photonics and electronics in transceivers facilitates energy-efficiency, bandwidth acceleration and a route to radical miniaturization. We present and implement a wafer-to-wafer integration method which combines electronic and photonic foundry technologies

Default Mode Network Connectivity and Social Dysfunction in Major Depressive Disorder

Though social functioning is often hampered in Major Depressive Disorder (MDD), we lack a complete and integrated understanding of the underlying neurobiology. Connectional disturbances in the brain’s Default Mode Network (DMN) might be an associated factor, as they could relate to suboptimal social processing. DMN connectional integrity, however, has not been explicitly studied in relation to social dysfunctioning in MDD patients. Applying Independent Component Analysis and Dual Regression on resting-state fMRI data, we explored DMN intrinsic functional connectivity in relation to social dysfunctioning (i.e. composite of loneliness, social disability, small social network) among 74 MDD patients (66.2% female, Mean age = 36.9, SD = 11.9). Categorical analyses examined whether DMN connectivity differs between high and low social dysfunctioning MDD groups, dimensional analyses studied linear associations between social dysfunction and DMN connectivity across MDD patients. Threshold-free cluster enhancement (TFCE) with family-wise error (FWE) correction was used for statistical thresholding and multiple comparisons correction (P < 0.05). The analyses cautiously linked greater social dysfunctioning among MDD patients to diminished DMN connectivity, specifically within the rostromedial prefrontal cortex and posterior superior frontal gyrus. These preliminary findings pinpoint DMN connectional alterations as potentially germane to social dysfunction in MDD, and may as such improve our understanding of the underlying neurobiology

Themaboek Roze Vleeskalveren

De roze vleeskalverhouderij staat vanaf eind 80-er jaren in de belangstelling. Aanleiding waren enerzijds de kanttekeningen die geplaatst werden bij de individuele huisvesting en de eenzijdige voeding van blanke vleeskalveren en anderzijds de hoge productiekosten. Omdat de kennis over de productie van roze kalfsvlees beperkt was, is in 1990 op het proefbedrijf van het PR, de Waiboerhoeve, een proefaccommodatie voor 320 kalveren gebouwd. In de periode 1991 t/m 1995 is het project ‘pro-ductie alternatief kalfsvlees’ uitgevoerd. Dit onderzoek is gefinancierd door het Landbouwschap, Ministerie LNV en Produktschap voor Vee en Vlees. In dit project zijn de voeding en de geschiktheid van verschillende typen kalveren uitgebreid onderzocht. De onderzoekresultaten zijn beschreven in PR-publicaties. Daarnaast was er behoefte de tot nu toe verkregen kennis in één publicatie te bundelen. Dit heeft geresulteerd in een themaboek voor de Roze vleeskalverhouderij. In dit themaboek worden de onderzoekresultaten kort weergegeven gekoppeld aan een praktisch advies. Naast het onderzoek wordt ook aandacht besteed aan o.a. huisvesting, wetgeving en diergezondheid

Contributing factors to advanced brain aging in depression and anxiety disorders

Depression and anxiety are common and often comorbid mental health disorders that represent risk factors for aging-related conditions. Brain aging has shown to be more advanced in patients with major depressive disorder (MDD). Here, we extend prior work by investigating multivariate brain aging in patients with MDD, anxiety disorders, or both, and examine which factors contribute to older-appearing brains. Adults aged 18–57 years from the Netherlands Study of Depression and Anxiety underwent structural MRI. A pretrained brain-age prediction model based on >2000 samples from the ENIGMA consortium was applied to obtain brain-predicted age differences (brain PAD, predicted brain age minus chronological age) in 65 controls and 220 patients with current MDD and/or anxiety. Brain-PAD estimates were associated with clinical, somatic, lifestyle, and biological factors. After correcting for antidepressant use, brain PAD was significantly higher in MDD (+2.78 years, Cohen’s d = 0.25, 95% CI −0.10-0.60) and anxiety patients (+2.91 years, Cohen’s d = 0.27, 95% CI −0.08-0.61), compared with controls. There were no significant associations with lifestyle or biological stress systems. A multivariable model indicated unique contributions of higher severity of somatic depression symptoms (b = 4.21 years per unit increase on average sum score) and antidepressant use (−2.53 years) to brain PAD. Advanced brain aging in patients with MDD and anxiety was most strongly associated with somatic depressive symptomatology. We also present clinically relevant evidence for a potential neuroprotective antidepressant effect on the brain-PAD metric that requires follow-up in future research

Enhanced amygdala reactivity to emotional faces in adults reporting childhood emotional maltreatment

In the context of chronic childhood emotional maltreatment (CEM; emotional abuse and/or neglect), adequately responding to facial expressions is an important skill. Over time, however, this adaptive response may lead to a persistent vigilance for emotional facial expressions. The amygdala and the medial prefrontal cortex (mPFC) are key regions in face processing. However, the neurobiological correlates of face processing in adults reporting CEM are yet unknown. We examined amydala and mPFC reactivity to emotional faces (Angry, Fearful, Sad, Happy, Neutral) vs scrambled faces in healthy controls and unmedicated patients with depression and/or anxiety disorders reporting CEM before the age of 16 years (n = 60), and controls and patients who report no childhood abuse (n = 75). We found that CEM was associated with enhanced bilateral amygdala reactivity to emotional faces in general, and independent of psychiatric status. Furthermore, we found no support for differential mPFC functioning, suggesting that amygdala hyper-responsivity to emotional facial perception in adults reporting CEM may be independent from top-down influences of the mPFC. These findings may be key in understanding the increased emotional sensitivity and interpersonal difficulties, that have been reported in individuals with a history of CEM.</p

All-optical switching due to state-filling in quantum dots

We report all-optical switching due to state-filling in quantum dots (QDs) within a Mach-Zehnder Interferometric (MZI) switch. The MZI was fabricated using InGaAsP/InP waveguides containing a single layer of InAs/InP QDs. A 1530-1570 nm probe beam is switched by optical excitation of one MZI-arm from the top. By exciting below the InGaAsP bandgap, we prove that the refractive index nonlinearity is only due to the QDs. The switching efficiency is 2 rad/(microW absorbed power). Probe wavelength insensitivity was obtained using a broad distribution of QDs.Comment: 12 page