93 research outputs found
Self-assembled strained nanostructures for light emission grown using molecular beam epitaxy
Get PDFIII-V nanostructures are widely researched for applications in dislocation-resistant light emitters for photonic integrated circuits, quantum computing and single photon emitters. The 0D nanostructures include quantum dots (QDs), dot in a well (DWELLs), sub-monolayer QDs and droplet epitaxy QDs, while 1D elongated structures include quantum dashes and nanowires (NWs). The optical properties of nanostructures can be controlled through size, composition, strain and band-offsets during epitaxial growth and can be tailored precisely to emit light with photon energies suited to the application, spanning 0.2-2.0 eV. This thesis explores two novel QD based light emitters in the visible and near-infrared wavelength regime. In the first part of the thesis, we demonstrate the growth and characterization of tensile strained Ge QDs and Ge NWs phase segregated in the III-V matrix via Volmer-Weber growth mode emitting at 1200 nm. The second part of the thesis demonstrates the dislocation tolerance of compressively strained InP QDs grown on lattice-matched GaAs and lattice-mismatched Si substrate via Stranski-Krastanov growth mode emitting at 713 nm.
The first part of the thesis explores the growth of tensile strained Ge QDs and NWs phase segregated in the III-V matrix. Epitaxial growth of phase segregated Ge nanostructures embedded within III-V compound semiconductors is a promising way to achieve a high biaxial tensile strain along with precise control of nanostructure density, size and morphology. Here we demonstrate growth of phase-segregated Ge quantum dots (QDs) and compare them to our previously reported Ge nanowires (NWs); both are strained to an In0.52Al0.48As matrix with a high biaxial tensile strain of 3.6%. Despite the similar growth conditions, there exist pronounced differences in the lateral size and planar density of Ge QDs and Ge NWs, with Ge QDs showing significantly larger size, lower density and structural anisotropy along the in-plane [1-10] direction. In addition to the difference in morphology, Ge QDs are shown to be more prone to plastic relaxation by formation of dislocations and stacking faults, which we attribute to their larger in-plane size. Finally, tensile Ge QDs are shown to exhibit strong room-temperature photoluminescence at 1176 nm, which is blueshifted from the case of Ge NWs.
In the second part of the thesis, we demonstrate epitaxial InP QDs on GaAs on Si virtual substrates with room-temperature photoluminescence (PL) intensity nearly identical to those grown on GaAs substrates. The similarity in PL characteristics is remarkable considering that the active region on the GaAs/Si virtual substrate has a threading dislocation density (TDD) of ~3×10^7 cm-2, as compared to the bulk GaAs substrate with TDD 50× improvement in the luminescence intensity of InP QDs annealed at ~700⁰C for 100 minutes without observable structural degradation or blue-shift in the PL spectrum.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2021-05-01The student, Pankul Dhingra, accepted the attached license on 2019-04-25 at 12:06.The student, Pankul Dhingra, submitted this Thesis for approval on 2019-04-25 at 12:16.This Thesis was approved for publication on 2019-04-25 at 14:10.DSpace SAF Submission Ingestion Package generated from Vireo submission #13914 on 2019-08-22 at 16:23:56Made available in DSpace on 2019-08-23T20:48:26Z (GMT). No. of bitstreams: 2
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Previous issue date: 2019-04-25Embargo set by: Seth Robbins for item 112387
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Mycotoxins in Foods: Occurrence, Regulatory Limits, and Methods of Analysis
No full textIntroduction
Mycotoxins are toxic compounds that are naturally produced by certain types of moulds (fungi). These are potent, naturally occurring toxic secondary metabolites generated by filamentous fungi (moulds). These compounds present a significant threat to both human and animal health by contaminating a wide array of agricultural commodities. Moulds capable of producing mycotoxins can develop on numerous foodstuffs, including cereals (maize, wheat, rice, barley), oilseeds (peanuts, soybeans), dried fruits (raisins, figs), nuts (almonds, walnuts, pistachios), spices (peppers, nutmeg), and coffee. Mould growth can occur either before or after harvest, as well as during storage, often under warm, damp, and humid conditions. Improper storage practices, such as inadequate drying, poor ventilation, and insect damage, can create favourable environments for mould growth
Fresh-cut fruits and vegetables – a review
Get PDFFresh cut products from fruits and vegetables are in great demand in local market as well as for export. It is very essential and critical to maintain the quality of fresh cut produce from the farmers’ field to the consumer. Fresh-cut processing involves careful selection of raw material variety, cultivar, maturity stage, washing, sanitising, peeling, deseeding, cutting, dicing, slicing, pre-treatment (anti-microbial, firming, flavour enhancer, etc.), packaging, storage at proper temperature, transportation, etc. Maintaining the quality and safety of fresh-cut produce is a challenge as deterioration processes take place due to ongoing biochemical and microbiological processes. The combination of sanitizing, packaging environment and temperature need to be optimized to maximize the quality (nutritional and sensory) and safety of the produce. The processors also need to know the spoilage causing organisms, such as pseudomonads, lactic acid bacteria, yeast, moulds, and fungi which can damage the quality of the produce. The knowledge of food borne pathogens and their sources is also important. The processors need to consider all the steps of the fresh-cut produce processing from the point of view of food safety as well as quality of the product
Post Harvest Technology of Garlic - A Review
No full textGarlic bulbs, valued for their flavour, command an extensive commercial importance because of their wide application in food and pharmaceutical preparations. The major producers of garlic in the world are China, India, South Korea, USA, Egypt and Spain. The world production of garlic in 2002 was 12.23 M tonne. Post harvest curing,. packaging, storage and processing of garlic are very important. Insects and fungi attack garlic bulbs during storage. Blue mold rot, dry rot and sprouting are the major causes of loss during storage. The storage loss can be minimized by following proper packaging and storage techniques. The pungent compounds of garlic responsible for the flavour suffer loss during processing. The processing techniques aim at minimizing the loss of pungent compounds and yielding shelf stable products. An attempt has been made to analyse the flavour chemistry of garlic, traditional and modern storage methods of garlic bulbs, methods of preparation of garlic paste, garlic extract, garlic oil, dehydrated garlic products, and "garlic pickle with special emphasis on the processing parameters and quality standards of end products. Analytical methods for the determination of volatile aromatic compounds in garlic bulbs and in its various preparations are also discussed
Post-Harvest Management of Fruits in India: A Review
No full textFruits play a vital role in supplementing human diets with essential minerals, vitamins, and fiber. India, with diverse climatic conditions, stands as the world’s second-largest producer of fruits and vegetables. Despite its significant contributions, the per capita production (200 g capita-1 day-1) remains below recommended levels of 230 g capita-1 day-1. The country’s horticulture sector has witnessed substantial growth, with a 33% share in agriculture output. India’s fruit production has surged, reaching 102.48 million tonnes in 2020-21. The export of fruits, valued at INR 62.19 billion in 2022-23, is dominated by mangoes, walnuts, grapes, bananas, and pomegranates. While the country has become a major player in fruit exports, capturing only 1% of the global market, there is growing acceptance due to advancements in cold chain infrastructure and quality assurance measures. However, post-harvest losses persist, ranging from 6% to 15%, necessitating effective strategies for reduction of post-harvest losses and improving shelf-life. Key challenges, including fragmented supply chains and inadequate infrastructure, are discussed alongside emerging opportunities presented by e-retailing and online platforms. Strategies for enhancing post-harvest management, supply chain efficiency, and adherence to marketing standards are outlined, with a focus on leveraging technology for sustainable growth. The paper also explores the import and export dynamics, the role of fruits in the Indian economy, importance of packaging, marketing standards of fruits and maximum residue limits (MRLs) to ensure fruit quality, safety, and consumer trust. The need for improved post-harvest management, infrastructure development, and skill enhancement emerges as critical for sustaining India’s fruit sector growt
Seaweeds – a potential source of food, feed and fertiliser
Get PDFMany communities in the world consume naturally growing and cultivated/ farmed seaweeds as food. Currently, commercial cultivation/farming produces more than 96% of seaweeds in the world and only around 3-4% is obtained from wild harvest (noncultivated). Naturally occurring and cultivated seaweeds are categorized into green, brown and red seaweeds, based on their pigmentation. More than 200 species of seaweeds are of commercial value, but only around 10 species of seaweeds are popularly cultivated. China, Indonesia, the Republic of Korea and the Philippines are the leading producers of cultured/ farmed species (viz. Eucheuma, Japanese kelp, Gracilaria, Unndaria pinnatifid); and Chile, China and Norway for wild species (mainly brown and red) and Chilean kelp. Seaweeds are rich in dietary fiber (polysaccharides), essential amino acids, major and micronutrients (minerals), vitamins etc. It has been reported that some species are a good source of plant growth regulators. Mainly, the people in China, Japan and Korea relish the soups, stews, flakes, coatings, snacks, etc., made from seaweeds. The use of seaweeds as human food in India is not very common. The second major use of seaweeds after food is the extraction of three important hydrocolloids (Agar, Alginate and Carrageenan). These are used as food additives and in many other industrial applications. A small portion of seaweed is used as an ingredient as livestock feed and fish feed. Seaweed meal and liquid extract of seaweed have been tried in conjunction with inorganic fertilizers with beneficial effects on crop yield, quality produce and soil health. Seaweed is an important marine resource and the coastline in India can be utilized to commercially cultivate seaweed species beneficial for human health and plants. Research is required in developing functional foods, health foods and nutraceuticals from seaweeds to improve the health and nutritional status of the human population. This paper briefly describes the status of production and utilization of seaweeds in different parts of the world
Evaluation of Centre of Gravity of Four Wheeled Trailer
No full textA four-wheeled trailer with flat platform was designed for fabrication of mobile agro-processing unit. The size of the trailer is 4270 mm x 2135 mm and its wheelbase is 263Omm. The location of the centre of gravity in longitudinal, transverse and vertical direction was determined by weighing method I technique. The total weight and the reaction on rear wheels were measured using a weighbridge. These reactions were used to locate the centre of gravity in longitudinal and transverse directions. The rear wheels were lifted and the net reaction on them was measured. The amount of weight transferred to the front wheels is dependent on the height of the centre of gravity. This concept was used to locate the height of the plane-containing centre of gravity. The centre of gravity was located with reference to the plane containing the wheel axles. It was observed to be 1139 mm behind front wheel axle, 618 mm above the wheel axles and midway (perpendicular to the axles) between the wheels
Feasibility Study of Maize Cobs as Throatless Gasifier Feedstock
No full textFuel properties of maize cob and its gasification feasibility in throatless downdraft gasifier were investigated.Performance of the throatless gasifier using producer gas from maize cobs was evaluated in terms of fuel consumptionrate, heating value of producer gas and gasification efficiency at different gas flow rates. Gasification efficiencyincreased with increasing gas flow rate, and was maximum (67.37 %) at specific gasification rate (SGR) of 169.95kg.h-1.m-2 and gas flow of 33.02 Nm3.h-1. Further increase in gas flow rate reduced gasification efficiency. Energybalance for the run had maximum efficiency. Each unit of energy input to the gasifier in the form of maize cobs wasconverted to 67.18 % chemical energy of producer gas and 16.82 % char residue, respectively. Sensible energy ofgas and char residue was 6.51 % and 0.11 %, respectively. The unaccounted losses were 9.38 per cent. Maize cobscould thus be successfully used as feedstock for throatless gasifier
Role and Importance of Rapid Methods in Evaluating Food Safety
No full textFood safety is a paramount concern for consumers, producers, processors, transporters, and virtually everyone involved in the food supply chain. Foodborne illnesses pose a significant global health threat, affecting millions worldwide. According to WHO 2022, every year an estimated 600 million people, nearly 1 in 10 individuals globally, fall ill due to contaminated food. Farmers and food processors adhere to established guidelines to ensure that the food they produce is safe and meets national and international standards. Regulatory agencies play a vital role in monitoring and overseeing the safety and quality of food traded in markets, protecting consumers’ interests
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