scholarly journals Estimation of the resonance amplitude in machines with inertia vibrator in the coast-down phase

2018 ◽  
Vol 19 (1) ◽  
pp. 102
Author(s):  
Grzegorz Cieplok
Keyword(s):  
Natural Frequency ◽  
The Body ◽  
Theoretical Research ◽  
Laboratory Model ◽  
Resonance Amplitude ◽  
Start Up ◽  
Approximation Formulas ◽  
Transient Resonance ◽  
Pass Through ◽  
Frequency Area

The work concerns mechanical systems with transient resonance formed as a result of an unbalanced rotating mass passing through an area of the system's natural frequency. In particular, this concerns over-resonant vibrating machines driven by inertia vibrators, which during start-up and coast-down pass through the natural frequency area related to the vibrating mass – flexible suspension system. The work analyses a system consisting of a soft-mounted machine body excited into vibrations by means of the inertia vibrator in order to designate the amplitude of resonant vibration, taking into consideration strong coupling between movements of the body and vibrator. The research results are presented in the form of nomograms and approximation formulas expressed in terms of relative parameters. The results of the theoretical research were verified on the laboratory model and industrial machines.

scholarly journals Graduate Students’ Behavioral Intention towards Social Entrepreneurship: Role of Social Vision, Innovativeness, Social Proactiveness, and Risk Taking

2021 ◽  
Vol 13 (11) ◽  
pp. 6386
Author(s):  
Bingyan Tu ◽  
Roni Bhowmik ◽  
Md. Kamrul Hasan ◽  
Ahmed Al Asheq ◽  
Md. Atikur Rahaman ◽  
...  
Keyword(s):  
Graduate Students ◽  
Risk Taking ◽  
Social Entrepreneurship ◽  
Entrepreneurial Orientation ◽  
Entrepreneurial Intention ◽  
The Body ◽  
Survey Method ◽  
Social Vision ◽  
Body Of Knowledge ◽  
Start Up

In prior studies, several researchers have adopted entrepreneurial orientation (EO) in determining students’ intention toward entrepreneurship, although the application of EO is scant in determining intention toward social entrepreneurship in existing literature. Hence, in consideration of this research gap, the current study empirically examines the influence of the dimensions of social entrepreneurial orientation (SEO): social vision, social proactiveness, innovativeness, and risk-taking motive on graduate students’ entrepreneurial intention toward social entrepreneurship-based business start-up. An online-based survey method was used to collect data from a sample of 465 students purposively who were studying at different universities in Bangladesh. A PLS-based SEM was applied to analyze the data and examined the proposed relationships in the conceptual model. The findings reveal that Graduate students’ social proactiveness, innovativeness, and risk-taking motive significantly affect their social entrepreneurial intention. However, students’ social vision does not have direct influence but has indirect influence on social entrepreneurial intention through their social entrepreneurial attitudes. The research contributes to the body of knowledge in the existing social entrepreneurship literature as well as provides practical implications for the policymakers, practitioners, and stakeholders working toward flourishing of social-based entrepreneurship, venture, and start-up.

Gliding Flight of the White-Backed Vulture Gyps Africanus

1971 ◽  
Vol 55 (1) ◽  
pp. 13-38 ◽  
Author(s):  
C. J. PENNYCUICK
Keyword(s):  
High Speed ◽  
Lift Coefficient ◽  
The Body ◽  
East African ◽  
Induced Drag ◽  
Gliding Flight ◽  
Vertical Speed ◽  
Statistical Sense ◽  
Pass Through ◽  
Comparison Measurements

1. Glide-comparison measurements were made on ten species of East African soaring birds using a Schleicher ASK-14 powered sailplane. Horizontal and vertical speed differences between bird and glider were measured by a photographic method, and used to estimate the bird's horizontal and vertical speeds relative to the air. The analysis refers to the white-backed vulture, since by far the largest number of measurements was obtained on this species. 2. A regression analysis using a two-term approximation to the glide polar yielded an implausibly high estimate of induced drag, which was attributed to a lack of observations at lift coefficients above 0.72. An amended glide polar was constructed assuming elliptical lift distribution and a maximum lift coefficient of 1.6 to define the low-speed end, while the high-speed end was made to pass through the mean horizontal and sinking speeds of all the experimental points. This curve gave a minimum sinking speed of 0.76 m/s at a forward speed of 10 m/s, and a best glide ratio of 15.3:1 at 13 m/s. It did not differ significantly (in the statistical sense) from the original regression curve. 3. In comparing the estimated circling performance, based on the amended glide polar, with that of the ASK-14, it was concluded that the rates of sink of both should be comparable, but that the glider would require thermals with radii about 4.3 times as great as those needed to sustain the birds. The conclusions are consistent with experience of soaring in company with birds. 4. In an attempt to assess the adaptive significance of the low-aspect-ratio wings of birds specializing in thermal soaring, the white-backed vulture's circling performance was compared with that of an ‘albatross-shaped vulture’, an imaginary creature having the same mass as a white-backed vulture, combined with the body proportions of a wandering albatross. It appears that the real white-back would be at an advantage when trying to remain airborne in thermals with radii between 14 and 17 m, but that the albatross-shaped vulture would climb faster in all wider thermals; on account of its much better maximum glide ratio, it should also achieve higher cross-country speeds. It is concluded that the wing shape seen in vultures and storks is not an adaptation to thermal soaring as such, but is more probably a compromise dictated by take-off and landing requirements. 5. The doubts recently expressed by Tucker & Parrott (1970) about the results and conclusions of Raspet (1950a, b; 1960) are re-inforced by the present experience.

Digestion in Ascidians and the Influence of Temperature

1929 ◽  
Vol 6 (3) ◽  
pp. 275-292
Author(s):  
N. J. BERRILL
Keyword(s):  
Enzyme Activity ◽  
Body Temperature ◽  
Digestive Enzymes ◽  
Alimentary Canal ◽  
The Body ◽  
Maximum Efficiency ◽  
Bile Pigment ◽  
Optimum Temperature ◽  
Different Temperatures ◽  
Pass Through

1. The mechanism of feeding and digestion in the Pyurid Ascidians Tethyum pyriforme americanum and Boltenia ovifera is described. 2. The structure and histology of the "liver" is described and it is shown that it is primarily an organ of secretion. 3. It is found that the only digestive enzymes are those poured into the gut by the liver, and consist of a powerful amylase, a protease, a very weak lipase, and also an invertase, a maltase, and a lactase. 4. The brownish pigment of the liver gives reactions with acids somewhat like those of bile pigment. There is no trace of bile salts, however, nor of cholesterol. 5. The amylase has an activity range from pH 6.0 topic pH 8.5 with an optimum near pH 7.5. The protease is active from pH 6.0 to above pH 10.0. A similar protease is secreted by Molgula citrina and Ascidia prunum. 6. The relative strengths of the amylase and protease are compared, the amylase being very much the stronger. 7. While experiments of brief duration indicate an optimum temperature for enzyme activity above 40° C, the more prolonged the experiments the lower does the optimum become. Whatever the optimum may be after an experiment of 2 hours' duration, it falls about 20° C. during the next 45 hours, if the experiments be so prolonged. 8. At 15° C. and at 10° C. the food takes about 35 and 55 hours respectively to pass through the alimentary canal, and at 50 C. somewhere between 70 and 90 hours. These temperatures approximately cover the normal range in temperature of the environment, and therefore of the animal itself. 9. From experiments lasting 33 hours the optimum temperature for enzyme activity was found to be about 17° C.; that is, within one or two degrees of the body temperature. From experiments lasting 57 hours the optimum temperature was found to be about 13° C ; that is, within three degrees of the body temperature. 10. These temperature optima not only represent the relative amounts of substrate converted at different temperatures, but also represent the absolute amounts converted and convertible. 11. The enzymes, amylase and protease, are two-thirds to three-quarters destroyed during their period of activity within the alimentary canal of the animal, and in order to utilise the remainder the digestion mixture would have to be retained within the canal for twice as long a time. 12. Therefore it seems probable that the organism in making such a compromise between a high activity of the enzyme and its economical use is working to a maximum efficiency; and it is possible that a permanent increase in the stability of the digestive enzymes would be turned to advantage through a more prolonged retention of the food within the gut.

Natural frequency modulation of a kinematically redundant planar parallel robot

2021 ◽  
pp. 095440622110524
Author(s):  
Jiawei Gu ◽  
Zhijiang Xie ◽  
Jian Zhang ◽  
Yangjun Pi
Keyword(s):  
Natural Frequency ◽  
Frequency Modulation ◽  
Natural Frequencies ◽  
Vibration Suppression ◽  
Excitation Frequency ◽  
Parallel Robot ◽  
Modulation Method ◽  
Kinematic Redundancy ◽  
Resonance Amplitude ◽  
Searching Method

When a parallel robot is equipped with kinematic redundancy, it has sufficient capabilities of natural frequency modulation through adjusting geometric configuration. To reduce resonance of a mechanism, this paper investigates the natural frequency modulation of a kinematically redundant planar parallel robot. A double-threshold searching method is proposed for controlling the inverse kinematics solution and keeping the natural frequencies away from the excitation frequency. The effectiveness of modulating the natural frequencies is demonstrated by comparing it with a non-modulation method. The simulation results indicate that, in all directions, the responses are coupled, and every order should be taken into consideration during natural frequency modulation. Compared to the non-modulation method, the proposed method can reduce the resonance amplitude to a certain extent, and the effect of vibration suppression is remarkable.

Concurrent Robust Product and Process Design

1999 ◽  
Author(s):  
Lars Lindkvist ◽  
Rikard Söderberg
Keyword(s):  
Process Design ◽  
Evaluation Criteria ◽  
Software Tool ◽  
The Body ◽  
Assembly Process ◽  
Critical Dimensions ◽  
Cad System ◽  
Start Up ◽  
Assembly Evaluation ◽  
Product And Process

Abstract This paper presents a method for assembly evaluation. The method uses two evaluation criteria, robustness and variation analysis, and is supported by a software tool developed by the authors. The robustness evaluation aims at detecting design and assembly solutions that are sensitive to variation and may cause problems during production. Using this method in early product and process design phases helps to find more robust concepts, resulting in shorter production start-up time and better precision. The method’s use is exemplified in a concept study of the assembly process of the door to the body of a (fictitious) jeep. The study shows that the proposed method can be used to obtain an objective comparison between different concepts. This comparison includes both general robustness and the expected variation in the critical dimensions. The results can be used, together with economical and practical aspects, to determine which concept is best suited for the assembly process. The software used is implemented in the MS Windows environment and has an JGES interface that enables the user to import CAD geometry from an arbitrary CAD system. It can perform different types of robustness evaluations as well as traditional variation analyses.

Cnidaria

1989 ◽  
Author(s):  
Heinz A. Lowenstam ◽  
Stephen Weiner
Keyword(s):  
Calcium Sulfate ◽  
Body Wall ◽  
Structural Features ◽  
The Body ◽  
Internal Space ◽  
Gravity Perception ◽  
Sessile Polyp ◽  
Gastrovascular Cavity ◽  
Mode Of Life ◽  
Pass Through

The phylum Cnidaria or Coelenterates includes sea anemones, jellyfish, hydras, sea fans, and, of course, the corals. With few exceptions they are all marine organisms and most are inhabitants of shallow water. In spite of the great variation in shape, size, and mode of life, they all possess the same basic metazoan structural features: an internal space for digestion (gastrovascular cavity or coelenteran), a mouth, and a circle of tentacles, which are really just an extension of the body wall. The body wall in turn is composed of three layers: an outer layer of epidermis, an inner layer of cells lining the gastrovascular cavity, and, sandwiched between them, a so-called mesoglea (Barnes 1980). All these features are present in both of the basic structural types: the sessile polyp and the free-swiming medusa. During their life cycle, some cnidarians exhibit one or the other structural type whereas others pass through both. Most Cnidaria have no mineralized deposits. The ones that, to date, are known to have mineralized deposits are listed in Table 5.1. They are found in both the free-swimming medusae and the sessile polyps. Not surprisingly, these have very different types of mineralized deposits. In the medusae they are located exclusively within the statocyst where they constitute an important part of the organism’s gravity perception apparatus. Interestingly the statoconia of the Hydrozoa, examined to date for their major elemental compositions only, are all composed of amorphous Mg-Ca-phosphate, whereas those of the Scyphozoa and Cubozoa are composed of calcium sulfate. Calcium sulfate minerals (presumably gypsum) are not commonly formed by organisms and the only other known occurrence is in the Gamophyta among the Protoctista. Spangenberg (1976) and her colleagues have expertly documented this phenomenon in the Cnidaria. (For a more detailed discussion of mineralization and gravity perception see Chapter 11.) The predominant mineralized hard part associated with the sessile polyps is skeletal. These can take the form of skeletons composed of individual spicules, spicule aggregates, or massive skeletons. They are composed of aragonite, calcite, or both.

Characteristics and Determinants of New Start-ups in Gujarat, India

2020 ◽  
Vol 1 (2) ◽  
pp. 1-25
Author(s):  
Ajay Kumar ◽  
Bhim Jyoti
Keyword(s):  
Sample Size ◽  
Regression Models ◽  
New Products ◽  
Small Sample ◽  
The Body ◽  
High Tech ◽  
Annual Sale ◽  
Factors Affecting ◽  
Start Up ◽  
Start Ups

Purpose: This study examines the relationship of socio-economic characteristics of start-ups with their size in Gujarat, India. It also assesses the determinants affecting the annual sale of start-ups. Methods: It includes primary information based on a survey of 120 founders of start-ups. Linear and semi-log linear regression models have been applied to assess the determinants of start-ups. Probit regression models have been considered to assess the factors affecting the annual sale of the start-ups. Results: Stage of start-up, the participation of founders in conferences, educational qualification, and new products launched by start-ups, professional connections of founders, source of funding, and support from incubator/accelerator/supporting organizations are found crucial determinants of start-up size in Gujarat. The annual sales of the start-ups are positively associated with stage of start-up, support from a mentor, team members, founder's academic qualification, and collaboration with national or international organizations, unskilled workers. Implications: Technology transfer and commercialization, development of new products, government regulations, the requirement of costumers, free rights for entrepreneurs, appropriate financial support for new entrepreneurs, transparency and clarity in government policies, the establishment of high-tech start-ups, and development of digital infrastructure, increase in R&D spending in research academia, and association of research institutions with entrepreneurs would be conducive to create an appropriate start-ups ecosystem and to reduce regional development disparities across Indian states. Subsequently, it would be helpful to increase sustainable development in India.  Originality: This study has used primary information of 120 founders of start-ups to assess the determinants, and the factors affecting annual sales of start-ups using the regression model in, Gujrat, India. Thus, it has an empirical contribution to the body of knowledge. Limitations: This study could not provide rational justifications on most factors that show an insignificant impact on start-ups due to the small sample size. Further research, therefore, may be considered to identify the association of start-up size with the variables using a large sample size in India.  

scholarly journals Research on the Resonance Characteristics of Rock under Harmonic Excitation

2019 ◽  
Vol 2019 ◽  
pp. 1-11
Author(s):  
Siqi Li ◽  
Shenglei Tian ◽  
Wei Li ◽  
Tie Yan ◽  
Fuqing Bi
Keyword(s):  
Resonance Frequency ◽  
Natural Frequency ◽  
Excitation Frequency ◽  
Harmonic Excitation ◽  
Theoretical Research ◽  
Transform Method ◽  
Factors Affecting ◽  
Least Action ◽  
Principle Of Least Action ◽  
Resonance Frequencies

In order to study the resonance characteristics of rock under harmonic excitation, two vibration models have been presented to estimate the natural frequency of rock encountered during the drilling. The first one is a developed single-DOF model which considers the properties and dimensions of the rock. The second one is a multi-DOF model based on the principle of least action. Subsequently, the modal characteristics, as well as the influence of excitation frequency, the mechanical properties, and dimensions of the rock on its resonance frequency, are analyzed by using FEM. Finally, the ultrasonic test on artificial sandstones and materials of drill tools are carried out indoor, and the FFT transform method is adopted to obtain their resonance frequencies. Based on the analysis undertaken, it can be concluded that the natural frequency of the rock increases with the change of vibration mode. For the same kind of rock, the resonance frequency is inversely proportional to mass, while for the different kinds of rocks, the mechanical parameters, such as density, elastic modulus, and Poisson’s ratio, determine the resonance frequency of the rock together. Besides, the shape of the rock is also one of the main factors affecting its resonance frequency. At last, the theoretical research results are further verified by ultrasonic tests.

scholarly journals Effects of Organ-Pipe Chamber Geometry on the Frequency and Erosion Characteristics of the Self-Excited Cavitating Waterjet

Energies ◽  
2020 ◽  
Vol 13 (4) ◽  
pp. 978
Author(s):  
Tengfei Cai ◽  
Yan Pan ◽  
Fei Ma ◽  
Pingping Xu
Keyword(s):  
Mass Loss ◽  
Natural Frequency ◽  
Pressure Sensors ◽  
The Self ◽  
Effective Length ◽  
Resonance Amplitude ◽  
Equivalent Length ◽  
Contraction Ratio ◽  
Organ Pipe ◽  
The Impact

Erosion experiments were performed to uncover the impact of organ-pipe chamber geometry on the frequency and erosion characteristics of self-excited cavitating waterjets. Jets emanating from self-excited nozzles with various organ-pipe geometries were investigated. The upstream and downstream contraction ratios of the organ-pipe resonator were changed respectively from 1.5 to 6 and 2 to 12. Pressure sensors and hydrophone were used to characterize jets’ frequency characteristics. Mass loss was also obtained in each of the configurations to assess the erosion performance. By tuning the self-excited frequency, the peak resonance was achieved using the nozzles with different geometries. Accordingly, the acoustic natural frequencies of various chamber geometries were obtained precisely. Results show that with increasing upstream and downstream contraction ratio of the organ-pipe chamber, the acoustic natural frequency increases monotonically due to the reduction of equivalent length, while the resonance amplitude and mass loss first increase and then decrease. There are optimum geometric parameters to reach the largest resonance amplitude and erosion mass loss: the upstream contraction ratio being between two and four, and downstream ratio being between four and seven. The effective length of the organ pipe can be calculated by the sum of the physical length and equivalent length to accurately obtain the acoustic natural frequency. Under the optimized parameters, the equivalent length can be estimated as 0.35D.

Histochemical observations on the occurrence of carbohydrates, lipids and enzymes in the daughter sporocyst of Cercaria bucephalopsis haimaena Lacaze-Duthiers, 1854 (Digenea: Bucephalidae).

Parasitology ◽  
1967 ◽  
Vol 57 (1) ◽  
pp. 79-86 ◽  
Author(s):  
B. L. James ◽  
E. A. Bowers
Keyword(s):  
Fatty Acids ◽  
Neutral Lipids ◽  
Anaerobic Respiration ◽  
Science Research ◽  
Body Cavity ◽  
The Body ◽  
Daughter Sporocyst ◽  
Laboratory Facilities ◽  
Pass Through ◽  
Higher Fatty Acids

The distribution of carbohydrates, lipids and enzymes in the daughter sporocyst and contained cercariae of Cercaria bucephalopsis haimaena Lacaze-Duthiers, 1854, is mapped and used as an indication of metabolism. It is concluded that host glucose, glycogen, fatty acids and neutral lipids are absorbed and pass through the syncytial tegument into the cellular sub-tegument. They are then either metabolized or passed into the body cavity and contained cercariae. Glucose seems to be either converted into glycogen and glycoproteins or metabolized anaerobically. The end products of anaerobic respiration are fatty acids and neutral lipids. These pass into the excretory system, which flushes them into the body cavity of the daughter sporocyst, from where they enter the body of the developing cercariae. In the cercariae they are deposited, together with host lipids, possibly as less toxic higher fatty acids or other stored lipids. The stored glycogen and lipids in the cercariae are probably utilized aerobically during the free-living existence. The transport of nutrients and excretory products across the cell membranes may be aided by alkaline phosphatase and esterase activity, as is the metabolism of carbohydrates and lipids. Acid mucopolysaccharide precursors appear to be synthesized in the dense cytoplasm of the mid-tegument of the daughter sporocyst and secreted into the host's visceral haemocoel. Acid phosphatase and esterase found in this region may be involved in the synthesis and also in the breakdown of complex incoming nutrients.We are grateful to Professor E. W. Knight-Jones for laboratory facilities and to the Science Research Council for a grant to one of us (E. A. B.) which made the work possible.

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