Studies on friction and formation of transfer layer when Al-4Mg alloy pins slid at various numbers of cycles on steel plates of different surface texture

In the present investigation, various kinds of textures, namely, unidirectional, 8-ground, and random were attained on the die surfaces. Roughness of the textures was varied using different grits of emery papers or polishing powders. Then pins made of Al-4Mg alloys were slid against steel plates at various numbers of cycles, namely 1, 2, 6, 10 and 20 under both dry and lubricated conditions using an inclined pin-on-plate sliding tester. The morphologies of the worn surfaces of the pins and the formation of transfer layer on the counter surfaces were observed using a scanning electron microscope. Surface roughness parameters of the plate were measured using an optical profilometer. It was observed that the coefficient of friction and formation of transfer layer during the first few cycles depend on the die surface textures under both dry and lubricated conditions. It was also observed that under lubricated condition, the coefficient of friction decreases with number of cycles for all kinds of textures. However, under dry condition, it ecreases for unidirectional and 8-ground surfaces while for random surfaces it increases with number of cycles

Continuation of limit cycles near saddle homoclinic points using splines in phase space

We present a new algorithm for continuation of limit cycles of autonomous systems as a system parameter is varied. The algorithm works in phase space with an ordered set of points on the limit cycle, along with spline interpolation. Currently popular algorithms in bifurcation analysis packages compute time-domain approximations of limit cycles using either shooting or collocation. The present approach seems useful for continuation near saddle homoclinic points, where it encounters a corner while time-domain methods essentially encounter a discontinuity (a relatively short period of rapid variation). Other phase space-based algorithms use rescaled arclength in place of time, but subsequently resemble the time-domain methods. Compared to these, we introduce additional freedom through a variable stretching of arclength based on local curvature, through the use of an auxiliary index-based variable. Several numerical examples are presented. Comparisons with results from the popular package, MATCONT, are favorable close to saddle homoclinic points.

Sustainable life cycles of natural-precursor-derived nanocarbons

Sustainable societal and economic development relies on novel nanotechnologies that offer maximum efficiency at minimal environmental cost. Yet, it is very challenging to apply green chemistry approaches across the entire life cycle of nanotech products, from design and nanomaterial synthesis to utilization and disposal. Recently, novel, efficient methods based on nonequilibrium reactive plasma chemistries that minimize the process steps and dramatically reduce the use of expensive and hazardous reagents have been applied to low-cost natural and waste sources to produce value-added nanomaterials with a wide range of applications. This review discusses the distinctive effects of nonequilibrium reactive chemistries and how these effects can aid and advance the integration of sustainable chemistry into each stage of nanotech product life. Examples of the use of enabling plasma-based technologies in sustainable production and degradation of nanotech products are discussed—from selection of precursors derived from natural resources and their conversion into functional building units, to methods for green synthesis of useful naturally degradable carbon-based nanomaterials, to device operation and eventual disintegration into naturally degradable yet potentially reusable byproducts.

Re-use of chicken litter across broiler cycles – managing the food-borne pathogen risk

Thus the objectives of this study can be broadly categorised as follows:-  Evaluate current practices adopted (e.g. litter pile-up) prior to re-use of litter for subsequent chicken cycles  To establish pathogen die-off that occurs during currently adopted methods of in-shed treatment of litter  To establish simple physical parameters to monitor this pathogen reduction and create an understanding of such reduction strategies to aid in-shed management of re-use litter  To carry out studies to assess the potential of the re-used litter (once spread) to support pathogens during a typical chicken production cycle.  To provide background data for the development of a simple code of practice for an in-shed litter pile-up process

On-farm Campylobacter and Escherichia coli in commercial broiler chickens: Re-used bedding does not influence Campylobacter emergence and levels across sequential farming cycles

Limitations in quality bedding material have resulted in the growing need to re-use litter during broiler farming in some countries, which can be of concern from a food-safety perspective. The aim of this study was to compare the Campylobacter levels in ceca and litter across three litter treatments under commercial farming conditions. The litter treatments were (a) the use of new litter after each farming cycle; (b) an Australian partial litter re-use practice; and (c) a full litter re-use practice. The study was carried out on two farms over two years (Farm 1, from 2009–2010 and Farm 2, from 2010–2011), across three sheds (35,000 to 40,000 chickens/shed) on each farm, adopting three different litter treatments across six commercial cycles. A random sampling design was adopted to test litter and ceca for Campylobacter and Escherichia coli, prior to commercial first thin-out and final pick-up. Campylobacter levels varied little across litter practices and farming cycles on each farm and were in the range of log 8.0–9.0 CFU/g in ceca and log 4.0–6.0 MPN/g for litter. Similarly the E. coli in ceca were ∼log 7.0 CFU/g. At first thin-out and final pick-up, the statistical analysis for both litter and ceca showed that the three-way interaction (treatments by farms by times) was highly significant (P < 0.01), indicating that the patterns of Campylobacter emergence/presence across time vary between the farms, cycles and pickups. The emergence and levels of both organisms were not influenced by litter treatments across the six farming cycles on both farms. Either C. jejuni or C. coli could be the dominant species across litter and ceca, and this phenomenon could not be attributed to specific litter treatments. Irrespective of the litter treatments in place, cycle 2 on Farm 2 remained campylobacter-free. These outcomes suggest that litter treatments did not directly influence the time of emergence and levels of Campylobacter and E. coli during commercial farming.

Microeconometric Studies on Unemployment and Business Cycles

Väitöskirja koostuu neljästä esseestä, joissa tutkitaan empiirisen työntaloustieteen kysymyksiä. Ensimmäinen essee tarkastelee työttömyysturvan tason vaikutusta työllistymiseen Suomessa. Vuonna 2003 ansiosidonnaista työttömyysturvaa korotettiin työntekijöille, joilla on pitkä työhistoria. Korotus oli keskimäärin 15 % ja se koski ensimmäistä 150 työttömyyspäivää. Tutkimuksessa arvioidaan korotuksen vaikutus vertailemalla työllistymisen todennäköisyyksiä korotuksen saaneen ryhmän ja vertailuryhmän välillä ennen uudistusta ja sen jälkeen. Tuloksien perusteella työttömyysturvan korotus laski työllistymisen todennäköisyyttä merkittävästi, keskimäärin noin 16 %. Korotuksen vaikutus on suurin työttömyyden alussa ja se katoaa kun oikeus korotettuun ansiosidonnaiseen päättyy. Toinen essee tutkii työttömyyden pitkän aikavälin kustannuksia Suomessa keskittyen vuosien 1991 – 1993 syvään lamaan. Laman aikana toimipaikkojen sulkeminen lisääntyi paljon ja työttömyysaste nousi yli 13 prosenttiyksikköä. Tutkimuksessa verrataan laman aikana toimipaikan sulkemisen vuoksi työttömäksi jääneitä parhaassa työiässä olevia miehiä työllisinä pysyneisiin. Työttömyyden vaikutusta tarkastellaan kuuden vuoden seurantajaksolla. Vuonna 1999 työttömyyttä laman aikana kokeneen ryhmän vuosiansiot olivat keskimäärin 25 % alemmat kuin vertailuryhmässä. Tulojen menetys johtui sekä alhaisemmasta työllisyydestä että palkkatasosta. Kolmannessa esseessä tarkastellaan Suomen 1990-luvun alun laman aiheuttamaa työttömyysongelmaa tutkimalla työttömyyden kestoon vaikuttavia tekijöitä yksilötasolla. Kiinnostuksen kohteena on työttömyyden rakenteen ja työn kysynnän muutoksien vaikutus keskimääräiseen kestoon. Usein oletetaan, että laman seurauksena työttömäksi jää keskimääräistä huonommin työllistyviä henkilöitä, jolloin se itsessään pidentäisi keskimääräistä työttömyyden kestoa. Tuloksien perusteella makrotason kysyntävaikutus oli keskeinen työttömyyden keston kannalta ja rakenteen muutoksilla oli vain pieni kestoa lisäävä vaikutus laman aikana. Viimeisessä esseessä tutkitaan suhdannevaihtelun vaikutusta työpaikkaonnettomuuksien esiintymiseen. Tutkimuksessa käytetään ruotsalaista yksilötason sairaalahoitoaineistoa, joka on yhdistetty populaatiotietokantaan. Aineiston avulla voidaan tutkia vaihtoehtoisia selityksiä onnettomuuksien lisääntymiselle noususuhdanteessa, minkä on esitetty johtuvan esim. stressin tai kiireen vaikutuksesta. Tuloksien perusteella työpaikkaonnettomuudet ovat syklisiä, mutta vain tiettyjen ryhmien kohdalla. Työvoiman rakenteen vaihtelu saattaa selittää osan naisten onnettomuuksien syklisyydestä. Miesten kohdalla vain vähemmän vakavat onnettomuudet ovat syklisiä, mikä saattaa johtua strategisesta käyttäytymisestä.

Performance studies on mechanical + adsorption hybrid compression refrigeration cycles with HFC 134a

This paper presents the results of an investigation on the efficacy of hybrid compression process for refrigerant HFC 134a in cooling applications. The conventional mechanical compression is supplemented by thermal compression using a string of adsorption compressors. Activated carbon is the adsorbent for the thermal compression segment. The alternatives of bottoming either mechanical or thermal compression stages are investigated. It is shown that almost 40% energy saving is realizable by carrying out a part of the compression in a thermal compressor compared to the case when the entire compression is carried out in a single-stage mechanical compressor. The hybrid compression is feasible even when low grade heat is available. Some performance indictors are defined and evaluated for various configurations.

Optical Studies of the Antarctic Glacio-Oceanic System

The Antarctic system comprises of the continent itself, Antarctica, and the ocean surrounding it, the Southern Ocean. The system has an important part in the global climate due to its size, its high latitude location and the negative radiation balance of its large ice sheets. Antarctica has also been in focus for several decades due to increased ultraviolet (UV) levels caused by stratospheric ozone depletion, and the disintegration of its ice shelves. In this study, measurements were made during three Austral summers to study the optical properties of the Antarctic system and to produce radiation information for additional modeling studies. These are related to specific phenomena found in the system. During the summer of 1997-1998, measurements of beam absorption and beam attenuation coefficients, and downwelling and upwelling irradiance were made in the Southern Ocean along a S-N transect at 6°E. The attenuation of photosynthetically active radiation (PAR) was calculated and used together with hydrographic measurements to judge whether the phytoplankton in the investigated areas of the Southern Ocean are light limited. By using the Kirk formula the diffuse attenuation coefficient was linked to the absorption and scattering coefficients. The diffuse attenuation coefficients (Kpar) for PAR were found to vary between 0.03 and 0.09 1/m. Using the values for KPAR and the definition of the Sverdrup critical depth, the studied Southern Ocean plankton systems were found not to be light limited. Variabilities in the spectral and total albedo of snow were studied in the Queen Maud Land region of Antarctica during the summers of 1999-2000 and 2000-2001. The measurement areas were the vicinity of the South African Antarctic research station SANAE 4, and a traverse near the Finnish Antarctic research station Aboa. The midday mean total albedos for snow were between 0.83, for clear skies, and 0.86, for overcast skies, at Aboa and between 0.81 and 0.83 for SANAE 4. The mean spectral albedo levels at Aboa and SANAE 4 were very close to each other. The variations in the spectral albedos were due more to differences in ambient conditions than variations in snow properties. A Monte-Carlo model was developed to study the spectral albedo and to develop a novel nondestructive method to measure the diffuse attenuation coefficient of snow. The method was based on the decay of upwelling radiation moving horizontally away from a source of downwelling light. This was assumed to have a relation to the diffuse attenuation coefficient. In the model, the attenuation coefficient obtained from the upwelling irradiance was higher than that obtained using vertical profiles of downwelling irradiance. The model results were compared to field measurements made on dry snow in Finnish Lapland and they correlated reasonably well. Low-elevation (below 1000 m) blue-ice areas may experience substantial melt-freeze cycles due to absorbed solar radiation and the small heat conductivity in the ice. A two-dimensional (x-z) model has been developed to simulate the formation and water circulation in the subsurface ponds. The model results show that for a physically reasonable parameter set the formation of liquid water within the ice can be reproduced. The results however are sensitive to the chosen parameter values, and their exact values are not well known. Vertical convection and a weak overturning circulation is generated stratifying the fluid and transporting warmer water downward, thereby causing additional melting at the base of the pond. In a 50-year integration, a global warming scenario mimicked by a decadal scale increase of 3 degrees per 100 years in air temperature, leads to a general increase in subsurface water volume. The ice did not disintegrate due to the air temperature increase after the 50 year integration.

Screening Cycles

We demonstrate how endogenous information acquisition in credit markets creates lending cycles when competing banks undertake their screening decisions in an uncoordinated way, thereby highlighting the role of intertemporal screening externalities induced by lending market competition as a structural source of instability. We show that uncoordinated screening behavior of competing banks may be not only the source of an important financial multiplier, but also an independent source of fluctuations inducing business cycles. The screening cycle mechanism is robust to generalizations along many dimensions such as the lending market structure, the lending rate determination and the imperfections in the screening technology.

Absorption-resorption heating cycles with the new working pairs R21-NMP and R21-DMA

The new working pairs, R21-NMP and R21-DMA, find potential application as working pairs for the single stage Resorption Heat Pump (RHP) and the Resorption Heat Transformer (RHT) cycles. A thermodynamic cycle analysis with these pairs shows that single stage RHPs have high COPs in their entire range of operation. RHTs show higher temperature boosts (up to 47 K) than the simple absorption heat transformers. Absorber temperatures of up to 400 K can be achieved in a single stage RHT system using R21 as the refrigerant. However, absorption-resorption systems have inherent limitations on the range of operating temperatures. Besides, they necessitate a higher pump work as compared to simple single stage absorption heating systems.

Thermodynamic modelling of absorption-resorption heating cycles with some new working pairs

This paper presents the results of a thermodynamic cycle analysis of single stage resorption heat pump (RHP) and resorption heat transformer (RHT) cycles with the new working pairs R22-NMP and R22-DMA. The coefficients of performance (COP) are correlated with the low grade source temperature, temperature at which useful heat is obtained and ambient temperature. The COPs are in the range 1.20–1.60 for the RHP mode and 0.25–0.45 for the RHT mode. Absorber temperatures (useful temperatures) as high as 50°C in the RHP mode and 87°C in the RHT mode have been obtained. It is observed that absorption-resorption systems are inflexible in their range of operating temperature and necessitate a higher pump work as compared with simple single-stage absorption heating systems. However, single stage RHTs show higher temperature boosts than simple absorption heat transformers.

A polynomial bound on the number of light cycles in an undirected graph

Let G be an undirected graph with a positive real weight on each edge. It is shown that the number of minimum-weight cycles of G is bounded above by a polynomial in the number of edges of G. A similar bound holds if we wish to count the number of cycles with weight at most a constant multiple of the minimum weight of a cycle of G.