• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 108
  • 88
  • 40
  • 8
  • 6
  • 6
  • 3
  • 3
  • 3
  • 3
  • 3
  • 3
  • 3
  • 2
  • 1
  • Tagged with
  • 331
  • 84
  • 55
  • 45
  • 34
  • 33
  • 33
  • 23
  • 21
  • 21
  • 19
  • 19
  • 18
  • 16
  • 16
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
81

Densidades de plantio e doses de potássio em abacaxizeiro Pérola sob irrigação / Density planting and potassium doses in pineapple Pérola under irrigation

Bueno, Juliana Azevedo Ruggiero [UNESP] 19 August 2016 (has links)
Submitted by JULIANA AZEVEDO RUGGIERO BUENO null (julianaruggiero@hotmail.com) on 2016-09-23T14:24:37Z No. of bitstreams: 1 tese impressão final 16-09-2016.pdf: 2183585 bytes, checksum: 37590f4054c6d05a361e5abd55ce8323 (MD5) / Rejected by Felipe Augusto Arakaki (arakaki@reitoria.unesp.br), reason: Solicitamos que realize uma nova submissão seguindo a orientação abaixo: O arquivo submetido não contém o certificado de aprovação fornecido pela Seção de Pós-Graduação. . Corrija esta informação e realize uma nova submissão contendo o arquivo correto. Agradecemos a compreensão. on 2016-09-27T13:58:02Z (GMT) / Submitted by JULIANA AZEVEDO RUGGIERO BUENO null (julianaruggiero@hotmail.com) on 2016-09-28T17:29:01Z No. of bitstreams: 1 tese impressão final com ata.pdf: 2609171 bytes, checksum: 3629b48f32051d2df6608c4faf330166 (MD5) / Approved for entry into archive by Ana Paula Grisoto (grisotoana@reitoria.unesp.br) on 2016-09-29T16:38:53Z (GMT) No. of bitstreams: 1 bueno_jar_dr_jabo.pdf: 2609171 bytes, checksum: 3629b48f32051d2df6608c4faf330166 (MD5) / Made available in DSpace on 2016-09-29T16:38:53Z (GMT). No. of bitstreams: 1 bueno_jar_dr_jabo.pdf: 2609171 bytes, checksum: 3629b48f32051d2df6608c4faf330166 (MD5) Previous issue date: 2016-08-19 / O plantio de abacaxi no Brasil é direcionado para o consumo in natura. Produzido principalmente no Norte e Nordeste, as variedades mais plantadas é o Pérola (com mais de 80% da área produzida) e o Smooth Cayenne. Este estudo evidenciou o efeito de diferentes densidades e doses de potássio na planta e no fruto de abacaxi Pérola em sistema irrigado, no Tocantins. O delineamento fez-se em blocos casualizados com parcelas subdivididas com quatro repetições. Os tratamentos principais constitui-se das doses de K (0, 8, 16 24 e 32 g planta - 1 de K2O) e os tratamentos secundários compostos das densidades de plantio que diferenciaram o espaçamento de plantas na mesma linha (30, 40, 50 e 60 cm). O plantio foi realizado em linhas duplas utilizando irrigação por gotejamento e as adubações de K executadas por fertirrigação. Avaliou- se a folha “D” do abacaxizeiro (comprimento, massa fresca da folha, composição mineral) e dos frutos (massa fresca com coroa, sem coroa e produtividade). Verificou-se que a folha “D” estava acima de 90 g e com mais de 100 cm, após 10 meses do plantio, estando apta a indução floral, concluindo-se que os tratamentos não interferiram no desenvolvimento do abacaxizeiro. Na avaliação química da folha “D”, houve significância na concentração de K, conforme se aumentou a dose de K no solo. Assim, as doses de K influenciaram na massa fresca do fruto sem coroa. As diferentes densidades influenciaram na massa fresca do fruto com e sem coroa e na produtividade. Portanto na variedade Pérola pode ter o adensamento utilizado até 41 mil plantas ha- 1, sem alterar a principal característica almejada, como também, frutos acima de 1.500 g, com a utilização de 8 g planta - 1de K2O, via fertirrigação, para a produção de frutos acima de 1.500 g. / The pineapple planting in Brazil is destined for fresh consumption. Produced mainly in the North and Northeast, the most planted varieties is the Pérola (with over 80% of the area produced) and the Smooth Cayenne. This study showed the effect of different densities and potassium levels in plant and pineapple fruit (Pérola) in the irrigation system in the Tocantins. The project was done in blocks with parcels subdivided design with four replications. The main treatments are K doses (0, 8, 16 24 and 32 g plant - 1 K2O) and compound secondary treatments of population densities that differentiated the spacing between plants on the same line (30, 40, 50 and 60 cm). The seedlings were planted in double rows using drip irrigation and fertilization of K performed by fertigation. Was evaluated sheet "D" pineapple (length, fresh weight of leaf mineral composition) and fruit (fresh pasta with the crown without crown and productivity). It was found that the "D" sheet was above 90 g and over 100 cm after 10 months of planting, before floral induction, concluding that the treatments did not affect the development of pineapple. In the chemical evaluation of "D" sheet had a significant concentration of K with increasing dose of K in the soil. Thus, the amount of K influences the fresh weight of fruit without a crown. The different densities influenced the mass of fresh fruits with and without crown and productivity. Therefore, the range Pérola can be used for densification up to 41,000 plants ha-1 without altering the desired main characteristic as well as obtaining fruit above 1500 g using 8 g plant - 1of K2O fertigation.
82

Efeito de densidades de plantio nas vari?veis morfol?gicas e de produ??o da bananeira ?BRS Princesa? e na din?mica de plantas daninhas / Planting density effect on morphological variables and production of banana "BRS Princess" and the dynamics of weeds

LANZA, Tomaz Ribeiro 01 February 2016 (has links)
Submitted by Jorge Silva (jorgelmsilva@ufrrj.br) on 2017-06-06T17:54:47Z No. of bitstreams: 1 2016 - Tomaz Ribeiro Lanza.pdf: 4430887 bytes, checksum: 399457041f3b433d4633da73992ed2e6 (MD5) / Made available in DSpace on 2017-06-06T17:54:47Z (GMT). No. of bitstreams: 1 2016 - Tomaz Ribeiro Lanza.pdf: 4430887 bytes, checksum: 399457041f3b433d4633da73992ed2e6 (MD5) Previous issue date: 2016-02-01 / FAPERJ / This study aimed to evaluate work in this plant densities on banana cultivation under phytotechnical aspects as well as the dynamics of weeds. The experiment was conducted in the experimental field of Horticulture - Plant Industry of UFRRJ, Serop?dica/RJ municipality in the agricultural year 2014/2015. micro propagated seedlings of banana type were used apple "BRS Princess" in a total of six treatments: 1200 (3.33 x 2.5 m), 1600 (2.5 x 2.5 m), 2000 (2.0 x 2.5 m), 2400 (1.67 x 2.5 m), 2800 (1.43 x 2.5 meters) and 3200 (1.25 x 2.5 m) plants per hectare arranged in experimental design a randomized block design with four replications. The experimental plot consisted of three rows with four banana plants in each, three plants of the center line, considered as useful plants. It evaluated monthly on the first and second production cycle, phytotechnical indicators of banana trees growing through the measurement of plant height, pseudostem diameter, leaf emergence and active leaves. For production parameters were measured quantitative aspects as bunch weight and fruit, stems parameters and standardization of fruit. Data were subjected to analysis of variance by F test and when significant models were adjusted for the biological phenomenon, the regression coefficient and the significance of the parameters. The phytosociological study of weed was made by sampling in installments, one one month after transplanting, and the following every 90 days, totaling six samples in 16 months of cultivation. They used square hollow 0.3 m side launched at random three times within each plot. The plants contained in the square were collected, identified and separated by species, counted and placed in an oven at 60 ? C for determination of dry matter. With the data obtained, the phytosociological indices were calculated: Relative density (De.R) Relative frequency (Fr.R) on Dominance (Do.R), importance value (IVI), the weed community. It was found that in the first cycle banana trees showed homogeneous development of the six treatments, except for diameter, with higher values for lower density treatments. For plants of the second cycle was observed significant influence of planting densities for vegetative parameters, with the exception of active leaves. As regards the production aspects, it was observed that the densities influence on the quantitative aspects of fruits such as grapes and fruit weight, but did not influence the standardization of fruit. Based on the phytosociology of weed it was possible to see significant changes in the dynamics of species, particularly as regards the reduction of species of the family of Poaceae, particularly P. maximum, and increased diversity and IVI more tolerant species to shading. As for the cultural control of banana trees on the weeds, it was observed that there was a lower density and dominance of weeds with the densification of culture. Based on the research results it can be concluded that the tested population densities did not affect vegetative aspects of growth of bananas the first cycle, but with significant effect on the second production cycle plants. It is noted that the planting densities influenced productive aspects of banana trees, and also favored higher productivities with plant density. It is also possible to conclude that the different banana planting densities influence the population dynamics of weeds as well as the cultural control of these. / Objetivou-se no presente trabalho avaliar densidades de plantas na cultura da banana sob aspectos fitot?cnicos bem como na din?mica de plantas daninhas. O experimento foi conduzido no campo experimental de Horticultura ? Setor de Fitotecnia da UFRRJ, munic?pio de Serop?dica/RJ no ano agr?cola de 2014/2015. Foram utilizadas mudas micro propagadas de banana tipo Ma?? ?BRS Princesa?, em um total de seis tratamentos: 1200 (3,33 x 2,5 m), 1600 (2,5 x 2,5 m), 2000 (2,0 x 2,5 m), 2400 (1,67 x 2,5 m), 2800 (1,43 x 2,5 m) e 3200 (1,25 x 2,5 m) plantas por hectare, dispostos em delineamento experimental de blocos ao acaso, com quatro repeti??es. A parcela experimental foi composta de tr?s linhas contendo quatro plantas de banana em cada, sendo tr?s plantas da linha central, consideradas como plantas ?teis. Avaliou-se, mensalmente, no primeiro e segundo ciclo de produ??o, indicadores fitot?cnicos de crescimento das bananeiras, atrav?s da mensura??o da altura da planta, di?metro do pseudocaule, emiss?o de folhas e folhas ativas. Para par?metros de produ??o foram mensurados aspectos quantitativos como peso do cacho e dos frutos, par?metros do enga?o e padroniza??o de frutos. Os dados foram submetidos a an?lise de vari?ncia pelo Teste F e quando significativos os modelos foram ajustados em fun??o do fen?meno biol?gico, do coeficiente de regress?o e da signific?ncia dos par?metros. O estudo fitossociol?gico de plantas daninhas foi realizado atrav?s de amostragens nas parcelas, sendo uma ap?s um m?s do transplantio, e as seguintes a cada 90 dias, totalizando seis amostragens em 16 meses de cultivo. Utilizaram-se quadrados vazados de 0,3 m de lado lan?ados ao acaso tr?s vezes dentro de cada parcela. As plantas contidas no quadrado foram coletadas, identificadas e separadas por esp?cie, contabilizadas e colocadas em estufa a 60?C para determina??o da massa da mat?ria seca. Com os dados obtidos, foram calculados os ?ndices fitossociol?gicos: Densidade relativa (De.R), Frequ?ncia relativa (Fr.R), Domin?ncia relativa (Do.R), ?ndice do valor de import?ncia (IVI), da comunidade de plantas daninhas. Verificou-se que no primeiro ciclo as bananeiras apresentaram desenvolvimento homog?neo nos seis tratamentos, exceto para di?metro, com valores superiores para os tratamentos de menor densidade. Para as plantas do segundo ciclo observou-se influencia significativa das densidades de plantio para os par?metros vegetativos, com exce??o de folhas ativas. Quanto aos aspectos de produ??o, observou-se que as densidades de plantio influenciaram nos aspectos quantitativos dos frutos, como peso do cacho e dos frutos, por?m n?o influenciaram na padroniza??o dos frutos. Com base na fitossociologia das plantas daninhas foi poss?vel verificar altera??es significativas na din?mica de esp?cies, principalmente no que se refere a redu??o de esp?cies da fam?lia das Poaceae, com destaque para P. maximum, e aumento da diversidade e do IVI de esp?cies mais tolerantes ao sombreamento. Quanto ao controle cultural das bananeiras sobre as plantas daninhas, foi poss?vel observar que houve menor densidade e domin?ncia de plantas daninhas com o adensamento da cultura. Com base nos resultados da pesquisa ? poss?vel concluir que as densidades populacionais testadas n?o afetaram aspectos vegetativos de crescimento das bananas do primeiro ciclo, por?m com efeito significativo nas plantas do segundo ciclo de produ??o. Observa-se que as densidades de plantio influenciaram aspectos produtivos das bananeiras, e tamb?m favoreceram maiores produtividades com o adensamento de plantas. Tamb?m ? poss?vel concluir que as diferentes densidades de plantio de banana interferem na din?mica populacional de plantas daninhas assim como no controle cultural dessas.
83

Produtividade e qualidade de híbridos de tomateiro do segmento salada de crescimento semideterminado em função de sistemas de poda e espaçamento / Yield and quality of tomato hybrids of standard segment of semi-determinate growth habit in function of pruning system and spacing

Leandro Valerim dos Santos 12 July 2017 (has links)
Atualmente a tomaticultura brasileira ostenta o título de cultivo com o maior custo de produção médio no país. Dentre algumas alternativas a fim de minimizar os elevados gastos está o uso de híbridos de crescimento semideterminado em sistema de meia-estaca, devido a menor necessidade de podas, insumos e mão de obra. Realizaram-se dois experimentos, em condições de campo aberto, com os objetivos de (a) determinar o efeito de diferentes sistemas de poda (P1, P2 e P3) e distintos espaçamentos entre plantas (E1 e E2) sobre a produção e seus componentes para o híbrido Silvety, de hábito de crescimento semideterminado do segmento Salada Longa Vida (SLV) (Experimento 1); e (b) avaliar o efeito de distintos sistemas de poda (P1 e P2) sobre a produção e seus componentes para os híbridos Silvety, Sagatan e H003, de hábito de crescimento semideterminado do segmento SLV (Experimento 2). Em ambos os experimentos adotou-se o delineamento em blocos ao acaso com os tratamentos em esquema fatorial 3 x 2 e quatro repetições. O experimento 1 foi conduzido em Jacuí, MG, de maio de 2015 a novembro de 2015, já o experimento 2 foi conduzido em Holambra, SP, de fevereiro de 2016 a agosto de 2016. Avaliaram-se o número total de frutos (NTF), a produção total por parcela (PTP), o número de frutos comercializáveis (NFC), a produção comercial (PCO), a produção por planta (PPP), a massa média dos frutos (MMF), o número de frutos por classe AAA, AA e A (NAAA, NAA e NA), a massa de frutos por classe AAA, AA e A (MAAA, MAA e MA), o número de hastes (NH) o número de inflorescências (NI), o número de frutos por inflorescência (NFI), o número de frutos com rachaduras cuticulares (CUT), o número de frutos ocos (OCO) e o número de frutos manchados (MAN). Nas condições em que os experimentos foram conduzidos e de acordo com os resultados obtidos conclui-se que no experimento 1, a poda P2e o espaçamento E1 mostraram-se os mais indicados para o híbrido Silvety. No experimento 2, novamente, a poda P2 mostrou ser a mais recomendada para os híbridos Silvety, Sagatan e H003. / Currently, the Brazilian tomato crop holds the title with the highest average cost of production in the country. Among the alternatives to minimize the high expenses, is the use of hybrids with semi-determinate growth habit in a training system of \"half-stakes\", due to the less need of pruning, inputs and labor. Two experiments were carried out under open field conditions, aiming to (a) to determine the effect of different pruning system (P1, P2 and P3) and spacing between plants (E1 and E2) on the production and its components for the Silvety hybrid, of semi-determinate growth habit of varietal segment Salad Extended Shelf Life (SLV) (Experiment 1), and (b) to evaluate the effect of pruning system (P1 and P2) on the production and its components for the Silvety, Sagatan and H003 hybrids, of semi- determinate growth habit of segment SLV (Experiment 2). In both experiments it was adopted the randomized block design with the treatments in a 3 x 2 factorial scheme, and four replications. Experiment 1 was conducted in Jacuí, MG, from May 2015 to November 2015, and Experiment 2 was conducted in Holambra, SP, from February 2016 to August 2016. There were assessed the total number of fruits (NTF), the total production per plot (PTP), the number of commercial fruits (NFC), the commercial production (PCO), the production per plant (PPP), the average mass of fruits (MMF), the number of fruits per classes AAA,AA and A (NAAA, NAA and NA), the mass of fruits per classes AAA, AA and A (MAAA, MAA and MA), the number of stems (NH), the number of clusters (NI), number of fruits per cluster (NFI), number of fruits with micro-cracking (CUT), number of hollow fruits (OCO), number of fruits with blotchy (MAN). Under the conditions that the trials were conducted and according to the results obtained, it was concluded that in experiment 1, the pruning system P2 and E1 spacing were the most suitable for Silvety hybrid. In experiment 2, again, the pruning system P2 showed to be the most recommended for Silvety, Sagatan and H003 hybrids.
84

Nitrogen requirements for cabbage (brassica olerecea capitata) transplants and crop response to spacing and nitrogen top-dressing

Semuli, Khabo Lemohang Harold 10 February 2006 (has links)
To determine the optimum nitrogen application level required for the production of good quality ‘Drumhead’ cabbage (Brassica oleracea var. capitata) transplants, a glasshouse experiment was conducted. Depending on water requirements, transplants were fertigated every two days (for the first four weeks) and every day (for the last two weeks) by floating trays in plastic tubs containing nutrient solution at 0, 30, 60, 90 and 120 mg•L-1 N until field capacity was reached. Increasing nitrogen from 0 to 120 mg•L-1 increased shoot and root mass of cabbage transplants with more dry mass being partitioned to the shoot than to the roots. Nitrogen at 120 mg•L-1 N produced greatest fresh and dry shoot mass, plant height, leaf area, leaf tissue nitrogen, net assimilation rate, relative growth rate and leaf mass ratio. Nitrogen at 90 mg•L-1 improved dry root mass, pulling success, specific leaf area and leaf area ratio. Greatest values of root: shoot ratio and root mass ratio were obtained at 0 mg•L-1 N. Nitrogen at 90 mg•L-1 was best as it produced transplants with more vigorous root growth which pulled out easily from the seedling trays. To determine the best combination of spacing and nitrogen top-dressing for improved cabbage production under local conditions, a field experiment was conducted. Cabbage ‘Copenhagen Market’ transplants were spaced at 30 x 50 cm, 40 x 50 cm or 50 x 50 cm and fertilized with nitrogen as top-dressing at 50, 100 or 150 kg•ha-1 N applied in two splits (fourth and eighth week after transplanting). There were no interactions between spacing and nitrogen top-dressing for all measured variables. Nitrogen and spacing did not influence dry matter production and leaf tissue nitrogen. Furthermore, spacing did not affect core height and yield (per unit area) of trimmed cabbage heads. Nitrogen at 100 kg•ha-1 produced the greatest head mass and yield for untrimmed cabbage heads. The 30 x 50 cm spacing produced the highest yield of untrimmed heads while 50 x 50 cm spacing produced heavier heads. For trimmed heads, 100 kg•ha-1 N again produced the greatest head mass, head diameter, head height, core diameter and yield. Spacing did not affect the yield for trimmed heads. However, 40 x 50 cm spacing improved head diameter, head height and head mass while core diameter was larger with 50 x 50 cm spacing. The split application of 100 kg•ha-1 N as top-dressing was best for head mass and yield (per unit area) for trimmed and untrimmed heads. Choice of spacing would depend on whether trimmed or untrimmed heads are targeted. / Dissertation (M Inst Agrar (Horticulture))--University of Pretoria, 2005. / Plant Production and Soil Science / unrestricted
85

Soybean Seeding Rate and Row Spacing Effects on Plant Establishment and Yield

Schmitz, Peder January 2018 (has links)
North Dakota soybean [Glycine max (L.) Merrill] management varies across the state, resulting in yield differences. Eight soybean seeding rates (starting at 197600 and increasing by 49400 live seed ha-1 increments) and row spacing (30 and 61 cm) were evaluated in 15 North Dakota environments in 2017-2018 to determine plant densities, seed yield, and plant loss, which were compared with soybean producer field data. Planting 30 cm row spacing yielded 183 kg ha-1 greater than 61 cm row spacing. On farm, maximum yields occurred at 414000 live seed ha-1 and final plant densities of 352000 plants ha-1. In research plots, 494000 live seed ha-1 had the highest yield. On farm, 8.9% plant loss occurred after plant establishment while research data observed 6.9% plant loss. North Dakota soybean producers should use narrow row spacing, use final plant density to estimate yields, and 444600 live seed ha-1 provided the highest net revenue. / North Central Soybean Research Program / North Dakota Soybean Council
86

Strategies for Improving Wheat and Soybean Production Systems in North Dakota

Schmitz, Peder E. Kenneth January 2021 (has links)
Planting date (PD), seeding rate (SR), genotype, and row spacing (RS) influence hard red spring wheat (HRSW, Triticum aestivum L. emend. Thell.) and soybean [Glycine max (L.) Merr.] yield. Evaluating HRSW economic optimum seeding rates (EOSR) is needed as modern hybrids may improve performance and have different SR requirements than cultivars. Two cultivars and five hybrids were evaluated in five North Dakota environments at two PDs and five SRs ranging from 2.22-5.19 million live seeds ha-1 in 2019-2020. Planting date, SR, and genotypes have unique yield responses across environments. Hybrid yield was the most associated with kernels spike-1 (r=0.17 to 0.43). The best hybrid yielded greater than cultivars in three environments. The EOSR ranged from 4.08-4.15 and 3.67-3.85 million seeds ha-1 for cultivars and hybrids, respectively. Hybrids are economical if seed prices are within $0.18 kg-1 of cultivars. In soybean, individual and synergistic effects of PD, SR, genotype relative maturity (RM), and RS on seed yield and agronomic characteristics, and how well canopy measurements can predict seed yield in North Dakota were investigated. Early and late PD, early and late RM, and two SRs (457 000 and 408 000 seed ha-1) were evaluated in 14 environments and two RS (30.5 and 61 cm) were included in four environments in 2019-2020. Individual factors resulted in 245 and 189 kg ha-1 more yield for early PD and late RM, respectively. The improved treatment of early PD, late RM, and high SR factors had 16% yield and $140 ha-1 more partial profit greater than the control. When including RS, 30.5 cm RS had 7% more yield than 61 cm RS. Adding 30.5 cm RS to the improved treatment in four environments resulted in 26% yield and $291 ha-1 more partial net profit compared to the control. A normalized difference vegetative index (NDVI) at R5 was the single best yield predictor, and stepwise regression using canopy measurements explained 69% of yield variation. North Dakota farmers are recommended to combine early PDs, late RM cultivars, 457 000 seed ha-1 SR, and 30.5 cm RS to improve soybean yield and profit compared to current management trends.
87

Evaluation of Row Patterns for Mid-South Corn Production Systems

Poulsen, Tyson T 10 August 2018 (has links)
Row patterns affected irrigated corn productivity when grown in the Mid-South region of the United States. Narrow (76 cm) row spacing increased grain yield 8% when compared to traditional wide (96-102 cm) row spacing. Twin rows (20-25 cm spacing) in a wide (96-102 cm) row pattern, produced similar grain yield as a traditional wide single row. At a normal plant density of 79,040 ha-1, traditional wide rows yielded 10.51 Mg ha-1, twin wide rows yielded 10.34 Mg ha-1, and the narrow rows yielded 11.33 Mg ha-1. Growing corn at various plant densities did not affect corn grain yield response to various row patterns. As a comparison the traditional wide rows and twin rows were similar in their yield, and the narrow rows performed better. Corn grain yields for the traditional 96-102 cm wide single rows were 11.20 Mg ha-1, wide 96-102 cm twin rows yielded 11.22 Mg ha-1, and narrow 76 cm rows produced 12.07 Mg ha-1. Row pattern had no effect on corn plant height, photosynthetically active radiation (PAR), leaf area index (LAI), SPAD, stalk diameter, and plant lodging in either study.
88

An Investigation into the Impact of Random Spacing Errors on Static Transmission Error and Root Stresses of Spur Gear Pairs

Handschuh, Michael James 23 July 2013 (has links)
No description available.
89

Evaluation of quinoa (Chenopodium quinoa Willd) at different spacings between furrows and plants in the Mamani community

Ferrufino Miranda, José 01 January 2003 (has links) (PDF)
This study addressed spacing between furrows and plants in the cultivation of the quinoa variety Patacamaya. This study took place from 1999 to 2000 in the Mamani community, Ingavi, La Paz, Bolivia. The Patacamaya variety is a cross between Samaranti (sweet) and Kaslala (bitter), with a vegetative cycle of 145 days (semi-early). It has large grains, is sweet, and has a high grain yield. The spaces between furrows were 40, 60, and 80 cm in an experimental design of randomly divided plots with four repetitions. The spaces between furrows were implemented in large plots and the plant spaces as sub-treatments in small plots. The results showed that the height of the plants were similar in all treatments except for T1 that was 35% lower compared with the other treatments. The highest grain yields occurred in treatment T6 with a value of 2,708.5 kg/ha, followed by T1 and T11. The lowest grain yields occurred in treatments T15, T10, and T5 with values of 1,124.3, 1561.4, and 1653.3 kg/ha, respectively.
90

A Finite Element Analysis on the Viscoelasticity of Postmenopausal Compact Bone Utilizing a Complex Collagen D-spacing Model

Cummings, Austin C 01 June 2015 (has links) (PDF)
The nanoscale dimension known as D-spacing describes the staggering of collagen molecules, which are fundamental to the biphasic makeup of bone tissue. This dimension was long assumed to be constant, but recent studies have shown that the periodicity of collagen is variable. Given that the arrangement of collagen molecules is closely related to the degree of bone mineralization, recent studies have begun to look at D-spacing as a potential factor in the ongoing effort to battle postmenopausal osteoporosis. The theoretical models presented by previous studies have only opted to model a single collagen-hydroxyapatite period, so the creation of an intricate computational approach that more exhaustively models a network of collagen and mineral is well-warranted. Sheep present an excellent opportunity to examine metabolic disorders, as their bone structure similar to that of the human skeleton. Six Rambouillet-cross ewes were used for the purpose of gathering experimental data. Three ewes underwent a sham surgery (controls), while an ovariectomy (OVX) was performed on the remaining three sheep. Each sheep was sacrificed after 12 months and their radius and ulna were harvested for atomic force microscopy and mechanical testing. Each sheep bone produced up to 25 beam samples that were available for analysis, and two were randomly selected from each test sheep. The cranial anatomical sector was selected for testing as it replicates the tensile loading condition characteristically experienced by collagen molecules and its exclusive examination removes any unintended variation due to bone section. Experimental D-spacing measurements were used in a finite element software, Abaqus, to create the ``Complex Model'': a large-scale, 2-D staggered array representation of collagen and hydroxyapatite periodicity. D-spacings intrinsic variability was mimicked through a Gaussian distribution that randomly determined periodic lengths based on provided experimental data. The model was generated with these random conditions for 2 x 100 units. Safeguards were implemented to ensure appropriate ratios of collagen to hydroxyapatite throughout the randomization. Collagen was assigned viscoelastic material properties originally developed by Dr. Frank Richter and modified by Miguel Mendoza. Hydroxyapatite was modeled as an elastic isotropic material. Four models were created using randomized D-spacings from control sheep and four separate models were created based on OVX sheep. Tangent delta--a damping characteristic--was recorded to evaluate bone viscoelasticity across four test frequencies: 1, 3, 9, and 15 Hz. Results strongly suggest that the Complex Model matches experimental findings more accurately than previous computational approaches. These results indicate the complicated network of many collagen units is an essential parameter of adequate modeling. A repeated measures analysis of variance was performed to examine the differences between control and OVX sheep. After adjusting for all other predictors, at the 1% significance level, after adjusting for all other variables, there is not enough evidence to convince this study that the Surgical Treatment alone has a significant impact on output tangent delta. This finding leads this study to conclude that OVX is fully accounted for within the Complex Model through the inclusion of its D-spacing, and the answers to bone's complicated mechanical properties during estrogen loss may lie in how OVX changes collagen viscoelasticity. Significant interactions were found between the Model Type and the Test Frequency. A Tukey-Kramer pairwise comparison was performed between Complex and Experimental data, which determined the Complex Model did not behave statistically differently from experimental findings at 15 Hz. This result suggests the Complex Model may begin to be validated to experimental results in a statistically meaningfully way that is a first for this style of FEA approach. The flexibility implemented in the randomization of the Complex Model welcomes refinement primarily in modeling viscoelasticity and fine-tuning the representation of mineralization. Through adjusting these material characteristics, the Complex Model may become an even more powerful tool in examining bone viscoelasticity and metabolic disorders.

Page generated in 0.059 seconds