Flat Cover Research Articles

Thermal evaluation of solar dryers and the effect on the antioxidant and some physicochemical properties of Agastache mexicana and Rosmarinus officinalis.

Lemon balm (Agastache mexicana) and rosemary (Rosmarinus officinalis) were dried using a mixed-mode solar dryer. A 23-factorial design was carried out: operation mode (mesh shade and direct irradiance), airflow (natural convection and forced convection), and type of flat plate solar collector cover (polycarbonate and glass). The drying kinetics of lemon balm and rosemary ranged from 4.5 to 6.5h and 4 to 7h, respectively, according to the operation mode of the solar dryer. The highest percentage of antioxidant activity in the 2,2-diphenyl-1-picrylhydrazil tests was lemon balm, with values between 88% and 93% (100µg/mL), and rosemary, 88% and 92% (100µg/mL). When forced convection was applied, solar collector thermal efficiency increased from 3.97%-5.11% to 17.20%-24.75%, dryer efficiencies ranged from 4.78% to 6.05%, and drying efficiencies between 14.17% and 44.23%. The lowest color difference (6.01) for lemon balm was shown with the mesh shade, forced convection, and glass cover collector, and for rosemary, the lowest color difference (12.87) resulted from using the mesh shade and natural convection; according to the analysis of variance, the cover collector did not affect significantly the color difference. Dehydrated lemon balm and rosemary could be used as an additive for medicinal, gastronomic, and food preservative applications. PRACTICAL APPLICATION: The results are significant for designing dryers for community centers in areas where the production and losses of fruits, vegetables, aromatic herbs, and edible flowers are high. The novelty of this research is to introduce a new product for the consumer; in this case, the traditional dried rosemary and lemon balm in powder form as a nutritional source, both for the preparation of remedies and for direct consumption in dishes, powders, or healthy pills and food supplements.

On weakly pullback flat S-posets

In 2005, Bulman-Fleming and Laan established an analog of the Lazard–Govorov–Stenström theorem in the convex of [Formula: see text]-posets, which shows that an [Formula: see text]-poset [Formula: see text] is strongly flat if and only if [Formula: see text]-preserves subpullbacks and subequalizers if and only if [Formula: see text] satisfies condition (P) and condition (E). Using subpullback diagrams, the equivalent descriptions of flatness and properties (P), (PWP) and (WP) were presented by Golchin and Rezaei in 2009. In this paper, we first give the definition of weak pullback flatness by using subpullback diagram. We then introduce condition (E[Formula: see text]) and prove that a right [Formula: see text]-poset [Formula: see text] is weakly pullback flat if and only if [Formula: see text] satisfies condition (P) and condition (E[Formula: see text]). At the same time, we correct an error in the paper “Strongly flat and po-flat [Formula: see text]-posets” by Shi, Comm. Algebra 33 (2005) 4515–4531. After that we investigate homological classification problems for cyclic [Formula: see text]-posets and Rees factor [Formula: see text]-posets using weak pullback flatness. Finally, we characterize the pomonoids over which every right [Formula: see text]-poset has a weakly pullback flat cover.

Duality between injective envelopes and flat covers

We establish a duality between injective envelopes and flat covers over a commutative Noetherian ring. One case of this duality states that a morphism is an injective envelope, if and only if its Matlis dual is a flat cover. We also show that if we swap injective envelopes and flat covers in this duality, neither implication is true in general.

Strength analysis of flat manhole cover in case of change of location and inclination angle of two mutually intersecting scratches

Mechanical damages of the main structural elements of the process equipment of hazardous production facilities are quite often detected during the revision process after repairs when assessing the quality of the work performed. One of the most common mechanical damages on the surface of parts and assemblies of technical devices includes scratches and risks. Significant scratches and risks that have a relatively large area and depth and limit the commissioning of the facility are subject to sampling and removal during re-repair. Superficial and non-extended scratches and risks do not belong to unacceptable defects, the technical device should not be taken into account, and further operation occurs with their presence. During further operation of the facility, such defects may not manifest themselves in any way, but may be high-voltage concentrators, which in the vast majority of cases are not critical. However, the presence of two or more scratches on the surface of the structural elements, their different location relative to each other, and therefore different mutual influence, can have a significant effect on the redistribution of zones and values of increased stresses on the surfaces where they are located. In the current regulatory and technical documents for diagnostics, these points are not considered, and accordingly are not taken into account. Therefore, the actual work is to perform a strength analysis of a flat manhole cover with two scratches, which have a different location on the surface, and a different angle of intersection relative to each other.

The Br = Br' question for some classifying stacks

In this paper we consider the Br = Br ′ question for classifying stacks by various group schemes. These are algebraic stacks that do not necessarily admit a finite flat cover by a scheme for which Br = Br ′ holds, hence are not amenable to the usual argument of pushing forward a twisted vector bundle. We provide two classes of examples satisfying Br ≠ Br ′ that do not arise from the scheme case. Communicated by Tony Varilly-Alvarado

Research on the Precision Measurement Method of Flat Screen Gap Based on Mobile Vision

In view of the problem that the measurement accuracy of screen gaps is affected by the R region of the transition rounded corner of the large-size flat back cover, a mobile vision system with dual linear motor synchronous drive is designed to realize precise positioning of monocular vision in 16 local image acquisition positions set in the R region. Full-size measurement of the R region is achieved using local information fusion to accurately measure the screen gap. First, to solve the problem of edge breaking and the blurring of local images, a region extraction and segmentation method based on block statistics is proposed to quickly obtain accurate outer edges. Then, an adaptive Hough line detection method based on dichotomy is proposed to accurately locate the outer edges. The experimental results show that the accuracy of region extraction and segmentation is up to 99.68% within 60 ms; the angle error and position error of line detection are less than 0.01° and 0.2 pixels, respectively. With optimal anti-interference performance, the proposed algorithm realizes the adaptive and accurate positioning of the outer edge within 200 ms; the measurement time and the measurement error of the measurement system are less than 6.0 s and 0.03 mm, respectively.

Effects of Straw Strip Covering on Yield and Water Use Efficiency of Potato cultivars with Different Maturities in Rain-Fed Area of Northwest China

The strip mulch of corn straw planting technique is widely used in the Northwest rain-fed agricultural region of China due to the region’s good soil moisture-temperature properties. However, the hydrothermal properties and yield effects of this planting technique on different potato varieties are not clear. Therefore, a field experiment was conducted for two years (2015 and 2016) in the rain-fed area of Northwest China, to study the effects of different mulching treatments on the yield and water use efficiency (WUE) of potato with different maturation characteristics (potato varieties Longshu 7 and LK99). A split-plot experimental design was used. The experiment included corn straw strip flat cover planting (SMF), plastic film mulching (PMF), corn straw strip ditch mulching and ridge planting (SMFR), straw flat fully covered (SMWF), and uncovered and flat planting (CK). The results showed that straw mulch and plastic film mulch had significant effects on yield and WUE (p < 0.05). Compared with CK, SMF significantly increased the yield by 3.75–63.17% in the late-maturing varieties, and increased the yield by 24.96–79.02% in the early-maturing varieties. Among the mulching treatments, compared with SMF, PMF made no significant difference in the yield and WUE between the late-maturing varieties in the normal year and the early-maturing varieties in the dry year, but the yield and WUE of the early-maturing varieties in the normal year significantly decreased by 17.25% and 18.44%, respectively, and the yield and WUE of the late-maturing varieties in the dry year significantly increased by 27.57% and 29.26% respectively. Compared with SMF, SMFR reduced yield by 1.44–13.62%; SMWF decreased the yield of late-maturing varieties by 25.94% (p < 0.05), and WUE decreased by 7.65–23.44% (p < 0.05). It can be seen that under this experimental condition, SMF is more suitable for early-maturing varieties and PMF is more suitable for late-maturing varieties.

Numerical simulation study on the heat dissipation characteristics of an air-cooled radiator

This article conducts numerical simulation calculations on the heat dissipation characteristics of an air-cooled radiator. The results show that under natural heat dissipation conditions, the maximum temperature of air-cooled radiators with flat heat dissipation covers decreases by 9.6% compared to radiators without heat dissipation covers, and the maximum temperature of air-cooled radiators with array raised heat dissipation covers decreases by 9.9%; Under forced air cooling conditions, the maximum temperature of an air-cooled radiator with a flat heat dissipation cover decreases by 12.7%, while the maximum temperature of an air-cooled radiator with an array raised heat dissipation cover decreases by 13.3%.

Filtration games and potentially projective modules

The notion of a $\mathcal C$-<em>filtered</em> object, where $\mathcal C$ is some (typically small) collection of objects in a Grothendieck category, has become ubiquitous since the solution of the Flat Cover Conjecture around the year 2000. We introduce

Development of a Custom-Made 3D Printing Protocol with Commercial Resins for Manufacturing Microfluidic Devices.

The combination of microfluidics and photo-polymerization techniques such as stereolithography (SLA) has emerged as a new field which has a lot of potential to influence in such important areas as biological analysis, and chemical detection among others. However, the integration between them is still at an early stage of development. In this article, after analyzing the resolution of a custom SLA 3D printer with commercial resins, microfluidic devices were manufactured using three different approaches. First, printing a mold with the objective of creating a Polydimethylsiloxane (PDMS) replica with the microfluidic channels; secondly, open channels have been printed and then assembled with a flat cover of the same resin material. Finally, a closed microfluidic device has also been produced in a single process of printing. Important results for 3D printing with commercial resins have been achieved by only printing one layer on top of the channel. All microfluidic devices have been tested successfully for pressure-driven fluid flow.

Surfaces on the Severi line in positive characteristic

Let k \mathbf {k} be an algebraically closed field, a minimal surface X X over k \mathbf {k} of maximal Albanese dimension is called on the Severi line if the ‘Severi equality’: K X 2 = 4 χ ( O X ) K^2_X=4\chi (\mathcal {O}_X) holds. We prove that X X is on the Severi line if and only if its canonical model X c a n X_{\mathrm {can}} admits a flat double cover over an Abelian surface.

Stress-strain condition of flat manhole covers under internal pressure in presence of mechanical defect with different dislocation on surface

One of the most common damage to the structural elements of vessels and apparatus of hydrocarbon processing plants is mechanical damage, which mainly occurs during repair and installation operations. One of the prerequisites for the occurrence of this type of defects is the use of a locksmith tool and other devices, tools and devices, upon contact of which with the surface of the elements to be repaired and mounted, risks, scratches, balls, nicks and other damage are formed. The vast majority in terms of the degree of occurrence on the surface of structural elements of all defects of a mechanical nature occupy scratches. There is practically no technical device operating in a hazardous production facility and does not have at least one of the elements of this type on the external surface. With respect to the surface on which the scratches are arranged, these defects can be both small geometrical dimensions and sufficiently extended. Such defects generally do not limit the life cycle of the object, but can have a significant effect on the redistribution of the stress-strain state in the element. The redistribution of the stress-strain state can serve as an initial stage for the generation of potential fracture sites from the concentration of increased stresses in these zones. Also, not only the presence of a scratch, but also the length, as well as the nature of the location on the surface of the element, can affect the stressed-deformed state of the element. Therefore, the actual work is a study of the change in the stress-deformed state of the flat manhole cover with a scratch, the arrangement of which on the surface has various options. In this work, the stress-strain state of the flat manhole cover is simulated depending on the change in the angle of inclination and the location of the scratch on it relative to the central zone.

On covers of acts over monoids with condition $$(PF'')$$ and envelopes of S-acts

In 2001, Enochs’ celebrated flat cover conjecture was finally proven, and the proofs have since generated a great deal of interest among researchers. In 2008, Mahmoudi and Renshaw initiated the study of flat covers of acts over monoids which concerned with the coessential epimorphisms. In this paper, we restrict our attention to $$(PF'')$$ -covers (coessential-covers that satisfy Condition $$(PF'')$$ ). We give a necessary and sufficient condition for cyclic act to have a $$(PF'')$$ -cover and give some classes of monoids that all cyclic right S-acts have a Condition $$(PF'')$$ -cover, we show that every weakly pullback flat cover is also $$(PF'')$$ -cover and every $$(PF'')$$ -cover is $$(P')$$ -cover, but the converses are not true. Besides we consider the $$\mathcal {PF''}$$ -cover (Enochs’ notion of a cover) and obtain some properties. Finally, we define and investigate the envelopes of S-acts.

Stress-Deformed Condition at Different Angle of Scratch Inclination on Flat Cover of Hatch-Blade

Defects of mechanical origin are quite often found on the structural elements of the devices of the production facilities of the fuel and energy complex. One of the most common mechanical defects is scratches and hairlines on the outer surface of the structural elements. The current regulatory and technical documentation establishes standards for the rejection of defects of various types, which provide for the decommissioning of objects with unacceptable defects for repair or subsequent dismantling. However, in most cases, mechanical defects such as scratches are within acceptable sizes and do not have a decisive effect on the life, reliability and safe operation of vessels and apparatus. However, the presence of such defects can change the stress-strain state of the object to a more unfavorable side, and therefore accelerate the process of accumulating damage at points of concentration of increased stresses. Subsequently, places with a concentration of increased voltages under certain operating conditions can be sources of premature destruction of the element and failure of the object as a whole. Therefore, the actual work is the simulation of the stress-strain state of the flat manhole cover with a scratch, having a different arrangement. In this work, the stress-strain state of the flat manhole cover is examined depending on the location of the scratch on it at a different angle relative to the vertical axis of symmetry of the cover.

Calculation of Strength of Facing Sheet of Flat Covers of Heat Exchangers Operating Under Vacuum

A procedure has been developed to calculate flat cover facing sheet fixed by electric rivets and welds along its outer and inner contours and loaded with external pressure. The calculation is based on the procedure for calculating key parameters of annular plates clamped along the inner and outer contours. The contours of two adjacent plates lying around the rivets join at a point that is equidistant from the adjacent rivets. Radial and annular stresses in the plates are calculated taking account of the load (design pressure) distributed uniformly over the surface of the plates and of the bending moments obtained from the condition that the angle between the normal and the curved middle surface of the annular plates is zero at the boundary of their joint. The inefficiency of using electric rivets, around which significant radial stresses develop due to their small diameter, is shown. It is recommended that the facing sheet be made in the form of annular plates fixed to the cover by annular welds, which will significantly reduce labor input.

Effects of plant growth and spacing on soil hydrological changes: a field study

Effects of plant growth on soil hydrological changes need to be considered for long-term vegetation management of geotechnical infrastructure. Most existing studies focused on one particular plant age. This study quantifies the effects of plant growth on the evolution of soil hydraulic properties and matric suction over time, through field monitoring and numerical soil–plant–atmosphere interaction modelling. A full-scale flat landfill cover in China was monitored for more than a year. Four 6 m × 6 m grass plots made of compacted silty sand were formed, three of which were vegetated with shrubs having different plant spacing (0·5, 0·8 and 1·1 m), while the fourth one was left grassed. In addition to monitoring matric suction changes, multiple soil cores were sampled to determine the root length density (RLD) and saturated hydraulic conductivity (ks) after 2, 4, 7 and 13 months of transplantation. Regardless of plant spacing, ks always reduced during the first 2–3 months of growth. When a threshold RLD of 2 cm/cm3 was reached, ks increased substantially. This was especially the case for closely spaced shrubs, whose roots were decayed. Suction preserved upon rainfall depended on the plant growth-induced changes in ks. Although closely spaced (0·5 m) shrubs preserved the most suction during the first 6 months of growth, the beneficial hydrological effects vanished after growing for 9 months because of the shrub growth-induced increase in ks. Instead, the widely spaced (1·1 m) shrubs, which showed the least increase in ks, preserved the most suction in later stages. Nonetheless, the spacing of shrubs did not affect the annual cumulative percolation of the landfill cover very significantly, which narrowly ranged between 3·1 and 4·7% of the annual precipitation during the monitoring period.

Turbulent heat exchange characterisics in sea ice ridges areas

The studies of the features of turbulent heat exchange were carried out for the first time in domestic practice near ice ridge areas of sea ice using an unmanned aerial vehicle (UAV) as part of the expedition "Transarktika-2019" onboard the R/V “Akademik Tryoshnikov”. An original measuring complex designed in AARI, was used to assess the characteristics of the ice surface (ice ridges, flat areas of ice). This made it possible to obtain comparative estimates of the albedo and surface temperature of different morphometric structures of the sections of the ice field, where the expedition's ice camp was organized. Measurements of air temperature and wind velocity were carried in the atmospheric surface layer on flat snow-covered areas of sea ice out from the windward and leeward sides of the ridge in parallel with the UAV flights. As a result of the experiments, it was found that the ice ridges areas have a lower albedo and surface temperature compared to neighboring areas of flat sea ice on average. Turbulent heat fluxes from the windward side of the hummock ridge exceed similar values recorded from the leeward side under conditions of unstable stratification in the atmospheric surface layer and exceed the fluxes calculated for conditions of flat ice on the sections with absence of hummocks, on average. In total, the nature and intensity of turbulent heat conduction in the ice ridges area differs from the analogous values observed on the flat sea ice cover. It is possible that the assessment of heat conduction with the atmosphere requires a certain revision, against the background (within the conditions) of thin first-year ice increasing which is more prone to hummocking than multi-year ice.

Quasi-Affineness and the 1-Resolution Property

Abstract We prove that, under mild hypothesis, every normal algebraic space that satisfies the $1$-resolution property is quasi-affine. More generally, we show that for algebraic stacks satisfying similar hypotheses, the 1-resolution property guarantees the existence of a finite flat cover by a quasi-affine scheme.

Failure Analysis on a Collapsed Flat Cover of an Adjustable Ballast Tank Used in Deep-Sea Submersibles

A flat cover of an adjustable ballast tank made of high-strength maraging steel used in deep-sea submersibles collapsed during the loading process of external pressure in the high-pressure chamber. The pressure was high, which was the trigger of the collapse, but still considerably below the design limit of the adjustable ballast tank. The failure may have been caused by material properties that may be defective, the possible stress concentration resulting from design/processing, or inappropriate installation method. The present paper focuses on the visual inspections of the material inhomogeneity, ultimate cause of the collapse of the flat cover in pressure testing, and finite element analysis. Special attention is paid to the toughness characteristics of the material. The present study demonstrates the importance of material selection for engineering components based on the comprehensive properties of the materials.

Cogeneration of energy in solar systems - a study case, Kosovo

&lt;p&gt;Nowadays the main goal of sustainable energy supply is the use of renewable energy sources and, in addition, the increased efficiency of the energy used. One possibility of using renewable energies is the use of solar energy through photovoltaic panels. Taking into account the meteorological characteristics of the country in which the study takes place, it appears that the use of photovoltaic panels will be available most of the time during the year. We applied a model of hybrid solar collectors for maintaining the cell temperature near 25°C by introducing a flat plate cover integrated with solar cells. This method represents a way to increase the efficiency of the solar collector. This will enable the production of electricity from the part of the photovoltaic panel incorporated into the solar collector, in which the water temperature will increase, and this heat from the water is due to the effect of sunlight and as a result of cooling the part of the photovoltaic panel. This represents an increase in the efficiency of the system and the main purpose of our analysis.&lt;/p&gt;