We study the dependence of the particle loading rate of a rubidium vapor cell magneto-optic trap (MOT). Using a trap depth determination of the MOT that relies on measurements of loss rates during optical excitation of colliding atoms to a repulsive molecular state, we experimentally determine the MOT escape velocity and show that the loading rate scales with escape velocity to the fourth power, or, equivalently, with the square of the trap depth. We also demonstrate that the loading rate is directly proportional to the background rubidium density. We thus experimentally confirm the loading rate model used in the literature since the invention of the MOT. In addition to confirming this long-standing conjecture, we show that the loading rate dependence can be used to reliably infer the trap depth and to tune the relative depth of a MOT (i.e., capture and escape velocities) when the background density is held fixed. The measurements have allowed an experimental determination of the relationship between capture and escape velocities in our MOTs of 𝑣𝑐=1.29(0.12)𝑣𝑒., Peer-reviewed article, Published.
A kinetic model is developed for cell differentiation in the fern gametophyte to test hypotheses on the role of spatially patterned plasmodesmata networks in development. Of particular interest is the establishment and maintenance of apical cell type in a single cell, with concurrent suppression of this character in all other cells (apical dominance). Steps towards understanding apical cell localization in geometrically simple gametophytes may shed light on the establishment and maintenance of apical meristems in higher plants. The model, based on the plasmodesmata maps of Tilney and colleagues and involving kinetics for a requisite minimum of two morphogens, successfully produces the apical/non‐apical cell differentiation patterns of normal development, and redifferentiation due to cell isolation, in six stages from 0–30 d of development. Our results indicate that increasing apical cell plasmodesmata number, as development progresses, is not required for effective transport across apical cell walls in maintaining apical dominance., Peer-reviewed article, Published. Received: 3 August 2001; Returned for revision: 12 November 2001; Accepted: 17 December 2001.
This paper investigates a novel approach for maintenance scheduling of volt-VAR control components (VVCCs) of distribution networks with the aid of new generation of volt-VAR optimization (VVO) solutions called quasi-real-time VVO. The new quasi-real-time VVO technique optimizes distribution network using advanced metering infrastructure (AMI) data of each quasi-real-time stage. As this VVO performs automatically and online, it is necessary for VVCCs to undergo maintenance without disturbing VVO performance. Moreover, the lost benefits that could be gained by online VVO have to be minimized. Hence, this paper proposes an AMI-based VVO consisting of a VVO engine and a maintenance scheduling engine (MSE) that operate in tandem to optimize distribution network and find the optimal maintenance scheduling of different VVCCs. To test the accuracy and the applicability of the proposed solution, a 33-node distribution feeder is employed. Furthermore, five different maintenance scenarios are investigated to check the proposed VVO performance. The results prove that the integration of VVO with MSE could be a reliable approach that can solve maintenance scheduling of VVCCs without interrupting and/or resetting VVO., Article, Published
We quantify fluctuations in protein expression for three of the segmentation genes in the fruit fly, Drosophila melanogaster. These proteins are representative members of the first three levels of a signalling hierarchy which determines the segmented body plan: maternal (Bicoid protein); gap (Hunchback protein); and pair-rule (Even-skipped protein). We quantify both inter-embryo and inter-nucleus (within a single embryo) variability in expression, especially with respect to positional specification by concentration gradient reading. Errors are quantified both early and late in cleavage cycle 14, during which the protein patterns develop, to study the dynamics of error transmission. We find that Bicoid displays very large positional errors, while expression of the downstream genes, Hunchback and Even-skipped, displays far more precise positioning. This is evidence that the pattern formation of the downstream proteins is at least partially independent of maternal signal, i. e. evidence against simple concentration gradient reading. We also find that fractional errors in concentration increase during cleavage cycle 14., Peer-reviewed article, Published. Received 30 September 2002; Accepted 12 December 2002; Published 16 December 2002.
Mammalian artificial chromosomes (MACs) provide a means to introduce large payloads of genetic information into the cell in an autonomously replicating, non-integrating format. Unique among MACs, the mammalian satellite DNA-based Artificial Chromosome Expression (ACE) can be reproducibly generated de novo in cell lines of different species and readily purified from the host cells' chromosomes. Purified mammalian ACEs can then be re-introduced into a variety of recipient cell lines where they have been stably maintained for extended periods in the absence of selective pressure. In order to extend the utility of ACEs, we have established the ACE System, a versatile and flexible platform for the reliable engineering of ACEs. The ACE System includes a Platform ACE, containing >50 recombination acceptor sites, that can carry single or multiple copies of genes of interest using specially designed targeting vectors (ATV) and a site-specific integrase (ACE Integrase). Using this approach, specific loading of one or two gene targets has been achieved in LMTK− and CHO cells. The use of the ACE System for biological engineering of eukaryotic cells, including mammalian cells, with applications in biopharmaceutical production, transgenesis and gene-based cell therapy is discussed., Peer-reviewed article, Publsihed.
The clandestine nature of illicit indoor marihuana production makes is difficult to measure the true extent of marihuana cultivation in a given policing jurisdiction. As a result, law enforcement must rely on estimations in order to understand the scale of the problem in terms of the number of growing operations, the number of growers, or the monetary value of the industry. This article describes an online estimation tool that was developed to aid law enforcement in the estimation of the annual production, domestic sale, exportation, and total value of marihuana produced in commercial growing operations within a given jurisdiction., Research article, Published.
The index of refraction of iodine vapour was measured in regions of anomalous dispersion. These measurements were made using a Michelson interferometer illuminated by a tunable dye laser, and encompass 30 GHz regions centered near 17 408.3 and 17 565.1 cm−1. These regions contained several rovibrational lines of the transition, and at a vapour pressure of 0.28 Torr (1 Torr = 133.3 Pa) the index of refraction near these lines was found to vary by a few parts in 107., Peer-reviewed article, Published.
Vegetative roofs have the potential to provide excellent external/internal sound isolation due to their high mass, low stiffness and their damping effect, and to provide a high level of sound absorption due to the low impedance of the vegetative substrate layer. The acoustical characteristics of vegetative roofs provide ecological contributions to the urban environment through a reduction of noise pollution from aircraft, elevated transit systems, and industrial noise. Vegetative roofs can reduce sound transmission into the interior of buildings, contributing to improved room acoustics through a reduction in noise and hence a reduction in distraction and stress (Connelly & Hodgson 2008). Through surface absorption, vegetative roofs will affect the propagation and build-up of positive and negative sounds and reduce reverberation in enclosed rooftop areas, altering the quality of the soundscape and the habitability of rooftops.
Vegetative roofs can be comprised of various material layers: root barrier, water reservoir/drainage layer, filter fabric, substrates and plants. The layer thought to have the most significant effect on the vegetative roof’s acoustical characteristics is the layer of the vegetation and substrate. The vegetative substrate is complex to characterize; it varies in terms of the depth of substrate, the substrate constituents and physical properties, the plant’s aerial biomass and root structure, as well as the dynamic in-situ microclimatic and conditions which vary over season and time., Article, Published.
Proceedings of the International Conference on Computational Science, ICCS 2012. In recent years the analysis of noise in gene expression has widely attracted the attention of experimentalists and theoreticians. Experimentally, the approaches based on in vivo fluorescent reporters in single cells appear to be straightforward and effective tools for bacteria and yeast. However, transferring these approaches to multicellular organisms presents many methodological problems. Here we describe our approach to measure between-nucleus variability (noise) in the primary morphogenetic gradient of Bicoid (Bcd) in the precellular blastoderm stage of fruit fly (Drosophila) embryos. The approach is based on the comparison of results for fixed immunostained embryos with observations of live embryos carrying fluorescent Bcd (Bcd-GFP). We measure the noise using two-dimensional Singular Spectrum Analysis (2D SSA). We have found that the nucleus-to-nucleus noise in Bcd intensity, both for live (Bcd-GFP) and for fixed immunstained embryos, tends to be signal-independent. In addition, the character of the noise is sensitive to the nuclear masking technique used to extract quantitative intensities. Further, the method of decomposing the raw quantitative expression data into a signal (expression surface) and residual noise affects the character of the residual noise. We find that careful masking of confocal images and use of appropriate computational tools to decompose raw expression data into trend and noise makes it possible to extract and study the biological noise of gene expression., Conference paper, Published.
Proceedings of the 12th North American Masonry Conference in Boulder, Colorado, May 17-20th, 2015. It is believed that one of the causes for unacceptably high death toll in the 2010 Haiti earthquake was due to use of low-strength hollow concrete blocks for masonry construction. After the earthquake, a team of BCIT faculty and students started to work on developing a low-cost nondestructive testing device for strength evaluation of concrete blocks which could be used in Haiti and other countries. The concept is based on the relationship between the compressive strength and the corresponding resonant frequency determined when a block is subjected to a mild impact. A simple block mould procured from Haiti was used to manufacture units with varying mix proportions typical of low-to medium-strength concrete blocks. In total, more than 70 concrete blocks and companion cylinders were made using13 different mix proportions to determine the compressive strength and other mechanical properties., Conference paper, Published.
In early development, genes are expressed in spatial patterns which later define cellular identities and tissue locations. The mechanisms of such pattern formation have been studied extensively in early Drosophila (fruit fly) embryos. The gap gene hunchback (hb) is one of the earliest genes to be expressed in anterior-posterior (AP) body segmentation. As a transcriptional regulator for a number of downstream genes, the spatial precision of hb expression can have significant effects in the development of the body plan. To investigate the factors contributing to hb precision, we used fine spatial and temporal resolution data to develop a quantitative model for the regulation of hb expression in the mid-embryo. In particular, modelling hb pattern refinement in mid nuclear cleavage cycle 14 (NC14) reveals some of the regulatory contributions of simultaneously-expressed gap genes. Matching the model to recent data from wild-type (WT) embryos and mutants of the gap gene Krüppel (Kr) indicates that a mid-embryo Hb concentration peak important in thoracic development (at parasegment 4, PS4) is regulated in a dual manner by Kr, with low Kr concentration activating hb and high Kr concentration repressing hb. The processes of gene expression (transcription, translation, transport) are intrinsically random. We used stochastic simulations to characterize the noise generated in hb expression. We find that Kr regulation can limit the positional variability of the Hb mid-embryo border. This has been recently corroborated in experimental comparisons of WT and Kr- mutant embryos. Further, Kr regulation can decrease uncertainty in mid-embryo hb expression (i.e. contribute to a smooth Hb boundary) and decrease between-copy transcriptional variability within nuclei. Since many tissue boundaries are first established by interactions between neighbouring gene expression domains, these properties of Hb-Kr dynamics to diminish the effects of intrinsic expression noise may represent a general mechanism contributing to robustness in early development., Peer-reviewed article, Published. Received: December 5, 2014; Accepted: December 15, 2014; Published: March 20, 2015.
Agriculture contributes significantly to anthropogenic greenhouse gases (GHGs), with estimates of agriculture's contribution ranging from 10% to 25% of total global GHG emissions per year. The science regarding mitigating (reducing and removing) GHGs through agriculture is conflicting and inconclusive. However, the severity and urgency of climate change and its potential effects on food security demonstrate that we must include mitigation within food system planning frameworks. In British Columbia, Canada, the provincial government has established significant GHG reduction targets for its agencies, and has called on local governments to reduce their carbon footprints through a charter and incentive, as well as through growth management legislation. At the same time, local governments, are giving increased attention to development of local/regional agri-food systems. However, GHG mitigation efforts do not yet seem to factor into local agri-food system discussions. Although frameworks for reporting agriculture GHGs exist, local government measurement of agriculture mitigation is hampered by a lack of agriculture GHG inventories, limited data availability, and the inherent variability in agriculture emissions and removals due to the dynamic nature of farm ecosystems. With the goal of informing local governments and food system planners on the importance of agriculture GHG mitigation, this paper (1) reviews the science of GHGs, (2) describes sources of agriculture GHG emissions and illustrates potential mitigation practices, (3) discusses the variability of agriculture mitigation science, (4) highlights the importance of agriculture GHG inventories, and (5) emphasizes the necessity for local agriculture mitigation strategies., Peer-reviewed article, Published. Submitted 18 April 2011 ; Revised 4 July 2011 and 1 August 2011 ; Accepted 2 September 2011 ; Published online 20 March 2012.