Collisions and drag in debris discs with eccentric parent belts

Context: High-resolution images of circumstellar debris discs reveal off-centred rings that indicate past or ongoing perturbation, possibly caused by secular gravitational interaction with unseen stellar or substellar companions. The purely dynamical aspects of this departure from radial symmetry are well understood. However, the observed dust is subject to additional forces and effects, most notably collisions and drag. Aims: To complement the studies of dynamics, we therefore aim to understand how new asymmetries are created by the addition of collisional evolution and drag forces, and existing ones strengthened or overridden. Methods: We augmented our existing numerical code "Analysis of Collisional Evolution" (ACE) by an azimuthal dimension, the longitude of periapse. A set of fiducial discs with global eccentricities ranging from 0 to 0.4 is evolved over giga-year timescales. Size distribution and spatial variation of dust are analysed and interpreted. The basic impact of belt eccentricity on spectral energy distributions (SEDs) and images is discussed. Results: We find features imposed on characteristic timescales. First, radiation pressure defines size cutoffs that differ between periapse and apoapse, resulting in an asymmetric halo. The differences in size distribution make the observable asymmetry of the halo depend on wavelength. Second, collisional equilibrium prefers smaller grains on the apastron side of the parent belt, reducing the effect of pericentre glow and the overall asymmetry. Third, Poynting-Robertson drag fills the region interior to an eccentric belt such that the apastron side is more tenuous. Interpretation and prediction of the appearance in scattered light is problematic when spatial and size distribution are coupled.Comment: Accepted for publication in A&A, 14 pages, 16 figure

Cozine Creek Restoration Project

Our Environmental Studies senior capstone class (ENVS 470) wrote and submitted an application for a $15,000 grant from the Oregon Watershed and Enhancement Board (OWEB) to restore a section of the college’s property along Cozine Creek. We worked in partnership with the Greater Yamhill Watershed Council (GYWC) and Upshot LLC, a local contractor, to develop a restoration plan. The initial step will be to control invasive species, mainly Himalayan blackberry and English ivy. We then will plant native species such as Oregon grape, salmonberry, and Indian plum. The site will have five treatment options including combinations of manual and chemical removal. Future ENVS classes will monitor the effectiveness of the treatment options, the growth and survival of native plants, and the effectiveness of deer exclusion devices. The ENVS department, GYWC, and community members will maintain the area through ongoing volunteer work parties. The grant will also fund a Cozine Creek Stewardship student internship position to help coordinate future efforts. The goal of this project is to restore the water quality and ecological integrity of the area, encourage proper usage of the property, and renew our connection to Cozine Creek, both for Linfield College and the surrounding community

Examining Water Quality along Cozine Creek

Water is an essential resource for all life. Water sustains ecological processes that are important to the survival of fish, vegetation, wetlands, and birds. It contributes to humans by providing drinking water, irrigation, and also is an inspiration for recreational, cultural, and spiritual practices. Anthropogenic activities affect water quality in various ways, and a significant portion of the human population is currently experiencing water stress. The quality of water, as well as its social and economic value, share a positive relationship. Therefore, as water quality becomes degraded by pollution, the environmental, social, and economic value also decrease. The recognition of the importance of safe water has created crucial policies in the United States and internationally. Our study looks specifically into the water quality of Cozine Creek, located in Yamhill County, Oregon. The goal of our study was to determine how water quality variables compared among our sampling sites in 2017 and across the years from 2011 to 2017. We used the definition of water quality as determined by measuring physical, chemical, and biological characteristics. We measured dissolved oxygen (DO), biochemical oxygen demand (BOD), pH, temperature, flow, turbidity, macroinvertebrates, bacterial counts, nutrients, and surrounding vegetation. To present a better understanding to the measurements of the water quality variables, we compared the measurements to the scientifically known parameters of healthy salmonid habitat, since the presence of salmon indicates a healthy watershed. Our data suggest that the overall quality of our three sites along Cozine Creek is poor, and there was little to no improvement of water quality when compared to previous years\u27 data. It is likely that the water quality can be attributed to agricultural and urban runoff possibly containing waste, storm water, pesticides, fertilizer, and other chemicals

Examining the sources of occupational stress in an emergency department

Background Previous work has established that health care staff, in particular emergency department (ED) personnel, experience significant occupational stress but the underlying stressors have not been well quantified. Such data inform interventions that can reduce cases of occupational mental illness, burnout, staff turnover and early retirement associated with cumulative stress. Aims To develop, implement and evaluate a questionnaire examining the origins of occupational stress in the ED. Methods A questionnaire co-designed by an occupational health practitioner and ED management administered to nursing, medical and support staff in the ED of a large English teaching hospital in 2015. The questionnaire assessed participants’ demographic characteristics and perceptions of stress across three dimensions (demand–control–support, effort–reward and organizational justice). Work-related stressors in ED staff were compared with those of an unmatched control group from the acute ear, nose and throat (ENT) and neurology directorate. Results A total of 104 (59%) ED staff returned questionnaires compared to 72 staff (67%) from the acute ENT/neurology directorate. The ED respondents indicated lower levels of job autonomy, management support and involvement in organizational change, but not work demand. High levels of effort–reward imbalance and organizational injustice were reported by both groups. Conclusions Our findings suggest that internal ED interventions to improve workers’ job control, increase support from management and involvement in organizational change may reduce work stress. The high levels of effort–reward imbalance and organizational injustice reported by both groups may indicate that wider interventions beyond the ED are also needed to address these issues

Development of decision support system for scheduling LPG supply-distribution at Teluk Semangka Port (Case study : PT. Pertamina Persero)

PT Pertamina (Persero) as the main contributor for LPG supply and distribution in Indonesia relies on the VLGC (Very Large Gas Capacity) for upstream transportation mode. All upstream activities are happened at Teluk Semangka Port, which is the main terminal for import supply and regional distribution throughout Java and Sumatra. The complexity in scheduling VLGC caused time consuming and high cost (demurrage cost and charter cost). Current report stated that through 2007 until 2013, there is a significant demurrage cost increased. This condition can jeopardized the supply and distribution process because of large budget allocation for covering the demurrage cost along with VLGC charter cost. A Decision Support System (DSS) is developed to generate schedule for each operated VLGC that both save time and gives the user recommendation in reducing cost. Several factors are considered in designing the DSS, such as lifting prioritization, demurrage cost, charter cost, and VLGC utilization. Besides its ability to generate complex schedule, an easy to use interface is designed for user to interact with the DSS. From several trials using real data taken from company database, it resulted five operated VLGCs as the best number of VLGCs to be operated. Therefore, it can be a recommendation for deciding the number of operated VLGCs in the following year

A study of the polysaccharide Psl in P. fluorescens by controlling the amount of proteins (putatively) involved in Psl synthesis

Polysaccharid synthesis locus (Psl) er et polysakkarid produsert av blant annet Pseudomonas aeruginosa, hvor det består av mannose, rhamnose og glukose. Psl er involvert i dannelsen av biofilm, og har vist seg å være viktig for modning av biofilm og cellefesting. Man har funnet Psl-genklynger i flere ikke-aeruginosa Pseudomonas-arter, deriblant i Pseudomonas fluorescens SBW25. Målet med denne studien var å få et innblikk i den mulige Psl-produksjonen i P. fluorescens ved å karakterisere genene i Psl-genklyngen og analysere innholdet i polysakkaridet som blir produsert. Genanalysene viste at Psl-genene med stor sannsynlighet ligger i samme operon, noe som lar oss sette inn en induserbar promoter for å kunne kontrollere genuttrykket. PmG5-promotoren ble derfor satt inn foran Psl operonet i ulike SBW25mucA-stammer ved bruk av homolog rekombinering. Ulike kombinasjoner av fjerning og overuttrykk av AlgA/AlgC/AlgD og Psl i P. fluorescens SBW25mucA-stammer ble laget for å kunne undersøke rollene til AlgA og AlgC i Psl-syntesen. Monosakkaridanalysene viste at Psl fra P. fluorescens sannsynligvis består av rhamnose, mannose og glukose. I tillegg indikerte resultatene at mangel på enten AlgA eller AlgC kan føre til en saktere Psl-produksjon. Dessuten ble det funnet høye glukosemengder for noen av stammene, som dermed trolig kan produsere en polyglukoseforbindelse når Psl-produksjonen er lav. Rollene til Psl, AlgC og AlgA ble undersøkt ved å se på forflytningsevnen til P. fluorescens og fenotypiske trekk. Det ble vist at mindre Psl operon-uttrykk på grunn av inaktivering av PmG5-promoteren gav kolonier med stor diameter når stammen manglet enten AlgA eller AlgC, sannsynligvis på grunn av en ubalanse i produksjonen av polysakkarider som dermed påvirker kolonistørrelsen. Videre ble det vist at overuttrykk av AlgC i kombinasjon med overuttrykk av Psl, dersom AlgA enten var villtype eller fjernet, gav de største koloniene i 0.5% agar, noe som kan indikere at for øke Psl-produksjonen må AlgC overuttrykkes i tillegg. Psl-negative stammer viste også at Psl produksjon trolig er viktig for vekst og biofilmdannelse, særlig ved kalde temperaturer. Til slutt ble fosfomannose isomerase-aktivitet (PMI) og fosfomannomutase-aktiviteten (PMM) forsøkt målt for P. fluorescens-mutanter. PslB har trolig PMI-aktivitet, slik som AlgA og WbpW, som begge er involvert i syntesen av forløpermolekyler til alginat og lipopolysakkarider. For å teste PMI-aktivitet ble det forsøkt utført et PMI-assay, som gav få resultater. Assayet krever dermed optimalisering for å få troverdige målinger fra P. fluorescens. AlgC har fosfomannomutase (PMM)-aktivitet, og er trolig nødvendig i produksjonen for forløpermolekylene som er involvert i Psl-produksjon. PMM-assayet ble utført med målbare tall, og resultatene indikerte tap av PMM-aktivitet ved overuttrykk av Psl-gener. Likevel var de målte enzymatiske aktivitetene for AlgC lave selv når PmG5-promoteren var aktivert, som indikerer at PMM-assayet også bør forsøkes å optimaliseres ved videre bruk i P. fluorescens.Polysaccharide synthesis locus (Psl) is an exopolysaccharide found in Pseudomonas aeruginosa, and consists of mannose, rhamnose, and glucose. Psl is involved in biofilm formation and has been found to be important for biofilm maturation and cell attachment. Psl gene clusters have been found in several non-aeruginosa Pseudomonas, such as in Pseudomonas fluorescens SBW25. This study aimed to get insight into the possible production of Psl from P. fluorescens by characterising the genes in the Psl gene cluster and analysing the exopolysaccharide content. The gene analysis revealed that the Psl genes are most likely within the same operon, allowing for the insertion of an inducible promoter to control gene expression. The PmG5 promoter can therefore be inserted in front of the Psl operon in different derivatives of SBW25mucA through homologous recombination. Different combinations of deletion and overexpressing AlgA/AlgC/AlgD and Psl in P. fluorescens SW25mucA strains were made, to further investigate the role of AlgA and AlgC on Psl synthesis. While monosaccharide analysis revealed that Psl from P. fluorescens likely consists of rhamnose, mannose, and glucose, the results also indicated that lack of either AlgA or AlgC seemed to slow down Psl production. In addition, some strains were found to have a high glucose content, possibly producing a polyglucose compound when Psl production is low. The role of Psl, AlgC, and AlgA was investigated on P. fluorescens motility and phenotypical traits. The result showed that less Psl operon expression due to inactivation of the PmG5 promoter causes large colonies when the strain is lacking either AlgA or AlgC, potentially due to an imbalance in exopolysaccharide production affecting the colony size. Furthermore, overexpressing AlgC along with Psl with deletion or wild-type AlgA seems to yield the largest colonies grown on 0.5% agar, possibly indicating that Psl overproduction is dependent on AlgC overproduction. Psl-negative strains also showed that Psl is likely to be important for growth and biofilm formation, especially in cold temperatures. Lastly, the phosphomannose isomerase (PMI) and phosphomannomutase (PMM) activity were attempted to be measured for the P. fluorescens mutant strains. PslB is thought to have PMM activity, similar to AlgA and WbpW in the synthesis of precursor molecules to alginate and lipopolysaccharides. To test PMI activity, a PMI assay was conducted, yielding few detectable results. Thus, the PMI assay would require further optimalisation for obtaining reliable measurements in P. fluorescens. AlgC has PMM activity and is thought to be required to produce the precursor molecules involved in Psl production in P. fluorescens. The PMM assay was conducted yielding reliable measurements, and the results indicated a loss of PMM activity when Psl genes were overexpressed. However, the low measured activity for AlgC, even when the PmG5 promoter was activated could indicate the need for optimalisation of the PMM assay as well for P. fluorescens

Development Of Decision Support System For Scheduling LPG Supply-Distribution At Teluk Semangka Port (Case Study: PT. Pertamina Persero)

PT Pertamina (Persero) as the main contributor for LPG supply and distribution in Indonesia relies on the VLGC (Very Large Gas Capacity) for upstream transportation mode. All upstream activities are happened at Teluk Semangka Port, which is the main terminal for import supply and regional distribution throughout Java and Sumatra. The complexity in scheduling VLGC caused time consuming and high cost (demurrage cost and charter cost). Current report stated that through 2007 until 2013, there is a significant demurrage cost increased. This condition can jeopardized the supply and distribution process because of large budget allocation for covering the demurrage cost along with VLGC charter cost. A Decision Support System (DSS) is developed to generate schedule for each operated VLGC that both save time and gives the user recommendation in reducing cost. Several factors are considered in designing the DSS, such as lifting prioritization, demurrage cost, charter cost, and VLGC utilization. Besides its ability to generate complex schedule, an easy to use interface is designed for user to interact with the DSS. From several trials using real data taken from company database, it resulted five operated VLGCs as the best number of VLGCs to be operated. Therefore, it can be a recommendation for deciding the number of operated VLGCs in the following year

Challenges Facing the Community in using Public Transport: A Case of Nkuhungu Ward in Dodoma City Council

The study of assessing challenges facing the community in using public transport was conducted at Nkuhungu ward in Dodoma city council The objectives of this study was to assess challenges facing the community in using public transport to evaluate availability of commuter buses examine the challenges and determine possible measures Methodology of study applied qualitative and quantitative data collected from respondents were summarized coded be analyzed and entered using statistic package for social science SPSS computer software used descriptive statistics to obtained means frequencies percentages and cross tabulations were used to obtain relationships between variables The result reveals that the availability of commuter buses in Nkuhungu is good about 68 8 and 1 0 is bad Also challenges facing passengers in using commuter buses majority 17 71 addressed that bad communication is one of big challenge that community faces and minority 4 17 injuries as a challenge About 25 of respondent addressed education and training as a possible measure and 4 17 suggested building bus stop near the community The study recommended that the ministry of home affairs and Sumatra should review their laws and policy and enforce them Service providers must provide good customer care Dodoma city councilor Sumatra and other stakeholders should increase bus stop and construct bus stop near the community Training should be provided to the service providers and their crew by stakeholders and owners of the buses concern with how to provide service work ethics and owners of the buses they must provide full time employment to physical mental and health peopl

Macroeconomic Determinants of Public Debt in Tanzania: Empirical Evidence and lessons for Post COVID-19 Recovery

This study examines the macroeconomic determinants of public debt in Tanzania for the 1970-2019 period employing the ARDL model.  The estimated results from the ARDL bound test reveal the presence of co-integration amongst the macroeconomic determinants of public debt. Moreover, in the short run, the ARDL shows that there is significant evidence that imports and government spending positively affect public debt while inflation rate affects public debt negatively, and the effect of foreign direct investment on public debt is statistically indistinguishable from zero. The study recommends that the governments of Tanzania should pursue sound macroeconomic policies that reduce public debt, while at the same time ensuring that resources are directed towards productive sectors of the economy in order to boost domestic production and increased revenue and export performance during the post- COVID 19. &nbsp

Twisted debris: how differential secular perturbations shape debris disks

Resolved images suggest that asymmetric structures are a common feature of cold debris disks. While planets close to these disks are rarely detected, their hidden presence and gravitational perturbations provide plausible explanations for some of these features. To put constraints on the properties of yet undetected planetary companions, we aim to predict what features such a planet imprints in debris disks undergoing continuous collisional evolution. We discuss the basic equations, analytic approximations and timescales governing collisions, radiation pressure and secular perturbations. In addition, we combine our numerical model of the collisional evolution of the size and spatial distributions in debris disks with the gravitational perturbation by a single planet. We find that the distributions of orbital elements in the disks are strongly dependent on grain sizes. Secular precession is differential with respect to involved semi-major axes and grain sizes. This leads to observable differences between the big grains tracing the parent belt and the small grains in the trailing halo. Observations at different wavelengths can be used to constrain the properties of a possible planet.Comment: 12 pages, 7 figure