Low-density Counterparts Research Articles

Energy distribution in 1D chains of foam disks subjected to low-velocity impact at different temperatures

A series of experiments is conducted to study energy transfer in a chain of foam disks as a function of temperature. These experiments use two different densities of closed-cell Polyvinyl Chloride foams as an array. A puncture testing machine impacts the chain at a velocity of 1 m/s at five different temperatures. Piezoelectric sensors capture the output and input forces of the chain during the impact, while high-speed cameras record the disk deformations. The chain’s energy retention is computed using disk deformations and loading forces. Results indicate that high-density foam chains exhibit significantly higher force and energy retention than low-density counterparts. Notably, the foam’s stiffness decreases with rising temperature, more prominently in higher-density foam. However, the proportion of energy retained by the chains remains relatively consistent across different temperatures. Additionally, both foam types show a pattern of exponential decay in energy retention along the chain. These insights offer implications for designing and optimizing energy-absorbing foam systems, paving the way for enhanced energy mitigation in low-velocity impact applications.

High-Density Atomically Dispersed Metals Activate Adjacent Nitrogen/Carbon Sites for Efficient Ammonia Electrosynthesis from Nitrate.

While electrocatalytic reduction of nitrate to ammonia presents a sustainable solution for addressing both the environmental and energy issues within the nitrogen cycle, it remains a great challenge to achieve high selectivity and activity due to undesired side reactions and sluggish reaction kinetics. Here, we fabricate a series of metal-N-C catalysts that feature hierarchically ordered porous structure and high-density atomically dispersed metals (HD M1/PNC). Specifically, the as-prepared HD Fe1/PNC catalyst achieves an ammonia production rate of 21.55 mol gcat-1 h-1 that is at least 1 order of magnitude enhancement compared with that of the reported metal-N-C catalysts, while maintaining a 92.5% Faradaic efficiency when run at 500 mA cm-2 for 300 h. In addition to abundant active sites, such high performance benefits from the fact that the high-density Fe can more significantly activate the adjacent N/C sites through charge redistribution for improved water adsorption/dissociation, providing sufficient active hydrogen to Fe sites for nitrate ammoniation, compared with the low-density counterpart. This finding deepens the understanding of high-density metal-N-C materials at the atomic scale and may further be used for designing other catalysts.

A multidimensional examination of phase separation in single-component fluids

A thermodynamic instability in a homogeneous fluid can lead to spontaneous formation of distinct domains within the fluid. This process involves not only the spatial redistribution of fluid density but also transient exchanges of pressure, temperature, and energy. However, classical theoretical frameworks, such as the Ginzburg–Landau and Cahn–Hilliard models, lack incorporation of these essential thermodynamic aspects. To investigate the dynamics of multiple physical fields during phase separation, we numerically solve a two-dimensional van der Waals fluid model. Thermodynamic consistency is demonstrated by verifying the coexistence curve. While the equilibrium pressure remains similar across the unstable region of the isotherm, we demonstrate that the energy in the system depends on the initial density. Although the majority of energy is stored as heat at typical values of the heat capacity, high-density domains contain less specific energy compared to their low-density counterparts due to interparticle attraction. Consequently, the transition of low-density domains into high-density through the process of coalescence releases excess energy, which redistributes in the form of longitudinal waves and heat. We also highlight the role of parameters, such as heat capacity and thermal conductivity, in less intuitive phenomena, including elevated temperature fluctuations and memory preservation.

Revealing the Impact of Critical Stellar Central Density on Galaxy Quenching through Cosmic Time

In a previous work, we investigated the structural and environmental dependence on quenching in the nearby universe. In this work, we extend our investigations to higher redshifts by combining galaxies from the Sloan Digital Sky Survey and The FourStar Galaxy Evolution surveys. In low density, we find a characteristic Σ1 kpc above which the quenching is initiated as indicated by their population-averaged color. Σ1kpccrit shows only a weak mass dependency at all redshifts, which suggests that the internal quenching process is more related to the physics that acts in the central region of galaxies. In high density, Σ1kpccrit for galaxies at z > 1 is almost indistinguishable from their low-density counterparts. At z < 1, Σ1kpccrit for low-mass galaxies becomes progressively strongly mass dependent, which is due to the increasingly stronger environmental effects at lower redshifts. Σ1kpccrit in low density shows strong redshift evolution with ∼1 dex decrement from z = 2.5–0. It is likely that at a given stellar mass, the host halo is on average more massive and gas-rich at higher redshifts; hence, a higher level of integrated energy from a more massive black hole (BH) is required to quench. As the halo evolves from the cold to hot accretion phase at lower redshifts, the gas is shock-heated and becomes more vulnerable to the feedback processes from active galactic nucleus as predicted by theory. Meanwhile, angular momentum quenching also becomes more effective at low redshifts, which complements a lower level of integrated energy from the BH to quench.

High-Density Communities and Infectious Disease Vulnerability: A Built Environment Perspective for Sustainable Health Development

High-density communities have proliferated globally during rapid urbanization. They are characterized by a high population density and limited per capita public spaces, making them susceptible to infectious disease risks. The impact of infectious diseases in these communities, as evident during the COVID-19 pandemic, underscores their vulnerabilities. Yet, research on disease prevention in high-density areas remains limited. This study aims to investigate the relationship between the built environment and the transmission of infectious diseases in high-density urban communities, with a particular focus on the lessons learned during the COVID-19 pandemic. Utilizing Shenzhen city as a case study, this study collected data on the built environment and epidemic trends and involved a generalized linear regression analysis, aiming to understand the key built environment factors that affect epidemic spread in high-density areas. The results from the study revealed that high-density communities experience higher rates of infectious disease transmission compared to their medium- to low-density counterparts. The significant factors identified include land use mixture and walkability, with land use mixture showing the most substantial impact on infection rates. Through a combination of qualitative analysis and empirical research, we constructed a conceptual framework linking containment measures, non-pharmaceutical interventions, and the built environment. The findings emphasize the significance to focus on the health development of high-density communities and offer valuable insights for tailored urban planning and built environment design. These insights are crucial for promoting the healthy and sustainable transformation of existing high-density communities.

Species transport in a variable-density turbulent mixing layer considering stratified instability

Mixing of miscible fluids with differing densities in turbulent mixing layers is of great importance in chemical engineering. In addition to the effect of density ratio R between two fluids, stratified instability will introduce additional complexity to turbulent mixing of species. We investigate this issue by performing direct numerical simulations of a stratified mixing layer involving two miscible fluids with R = 1, 3, and 6. We find the stronger decay of turbulence in the high-density stream in comparison with the low-density counterpart, which is attributed to the decrease in the shear rate and the increase in stratified instability. Moreover, it shows the dynamical connections between stably stratified mixing layers and wall-bounded turbulent flows, which can be supported by the hairpin vortical structures, the vertical profile of integral shear parameter S* in the low-density side (S* ≈ 10–30), and an inverse wave-number scaling for streamwise energy spectrum of velocity fluctuation. The statistical analysis of the budget of the mixture fraction variance shows that the turbulent mixing of species is significantly suppressed in the high-density side while enhanced in the low-density one, as a result of the larger reduction of turbulent production, turbulent flux, and a smaller reduction of dissipation in the high-density side. Finally, we find that the dissipation rate of the structure function of the mixture fraction variance is about four times larger than that of mixture fraction variance. These results can provide support for large eddy simulation of stratified turbulent mixing of miscible fluids with differing densities.

Ultrahigh-Density Double-Atom Catalyst with Spin Moment as an Activity Descriptor for the Oxygen-Reduction Reaction

One of the great challenges facing atomically dispersed catalysts, including single-atom catalysts (SACs) and double-atom catalysts (DACs), is their ultralow metal loading (typically less than 5 wt %), which limits their practical catalytic applications, such as in the oxygen-reduction reaction (ORR), which is crucial for hydrogen fuel cells and metal-air batteries. Although some important progress has been achieved in ultrahigh-density (UHD) SACs, reports on UHD DACs with stable uniform dispersion are still lacking. Herein, based on the experimentally synthesized ${M}_{2}{\mathrm{N}}_{6}$ motif ($M\phantom{\rule{0.25em}{0ex}}=\phantom{\rule{0.25em}{0ex}}\mathrm{Sc}$-$\mathrm{Zn}$), we theoretically demonstrate the existence of UHD DACs, with a metal loading of &gt;40 wt %, which are confirmed by systematic analyses of dynamic, thermal, mechanical, thermodynamic, and electrochemical stabilities. Furthermore, the ORR activities of the UHD DACs are comparable to or even better than those of their experimentally synthesized low-density counterparts, and the ${\mathrm{Fe}}_{2}{\mathrm{N}}_{6}$ and ${\mathrm{Co}}_{2}{\mathrm{N}}_{6}$ UHD DACs are located at the peak of the activity volcano with ultralow overpotentials of 0.31 and 0.33 V, respectively. Finally, the spin magnetic moment of the active center is found to be a catalytic descriptor for the ORR on DACs. Our work can stimulate the experimental exploration of ultrahigh-density DACs and provides an insight into the relationship between the ORR activity of DACs and their spin states.

Density-Induced Joule-Heating Characteristics of Nanocarbon Aerogels: Implications for Tunable Electrothermal Behaviors

An in-depth understanding of the electrothermal characteristics and behaviors of nanocarbon aerogels is crucial for optimizing their Joule-heating performance and expanding their applications. Modifying a single parameter of nanocarbon aerogels can reveal potential variations in Joule heating, which makes it a valuable area for investigation. This study explores reduced graphene oxide aerogels and reduced graphitized nanofiber aerogels with varying densities (14.9–31.7 mg·cm–3), fabricated using the hydrothermal method and polymer-assisted cross-linking method, to elucidate density-induced Joule-heating discrepancies. The critical step in aerogel preparation is the freeze-drying process, which yields structurally intact nanocarbon aerogels for Joule-heating experiments. Aerogels with higher densities displayed enhanced electrical and thermal conductivities (up to 24.9 S·m–1 and 0.882 W·m–1·K–1, respectively) compared to their lower-density counterparts, owing to the increased number of pathways available for electron/phonon transportation. The low-density aerogels exhibited more pronounced features in the heating temperature range (up to 117 °C) and efficiency (up to 46.5 °C·W–1), making them more suitable for energy-efficient applications. Despite variations in the density, all of the fabricated aerogels showed efficient electron hopping between the interconnected nanocarbons, which enabled uniform resistive heating throughout the aerogel entity. This work highlighted the importance of density control in altering the Joule-heating performance of nanocarbon aerogels for specific applications, which has far-reaching implications for optimizing the properties of other electrically conducting aerogel materials.

Effect of diet and rearing density on contest outcome and settlement in a field cricket

The ability to win fights is expected to be influenced by the rearing and nutritional conditions experienced by individuals. We hypothesized that crowded rearing conditions would foreshadow intense competition for resources in adult male Gryllus firmus (Scudder) field crickets and thus favour greater investment in mandibular weaponry. In line with prediction, males developed relatively larger weapons in crowded rearing conditions but this investment did not translate into greater success in contests against size-matched males that were reared singly. Rather, we found that low-density males were more likely to defeat high-density males under some experimental conditions, possibly because low-density males are more aggressive. Overall, our strongest observed effect was that males with larger weaponry were more likely to win contests, independent of rearing density. We also manipulated the adult diet of males to test the hypothesis that greater fat loads, and thus potentially greater stamina, would improve success in contests. Contrary to prediction, increased fat load did not increase a male’s probability of winning a contest possibly because fights in field crickets are too short to invoke stamina. Broadly speaking, animals decide whether to give up in a fight by assessing either their own (self-assessment) resource-holding potential (RHP) or by assessing a combination of their own and their opponent’s RHP (mutual assessment). Our study lends some support to the hypothesis that male G. firmus crickets decide to persist in a fight by assessing their own RHP rather than via mutual assessment. Animals fight each other for access to, and control of, resources that they require for survival and reproduction (e.g. food, shelter, and mates). Although considerable empirical research has shown that individuals having a larger body size or weapons generally possess greater fighting ability—resource-holding potential (RHP)—and are thus typically more successful in combat, the factors contributing to the development of an individual’s RHP have received less attention. One potential environmental factor dictating RHP is population density; however, the effect of density on RHP is difficult to predict. Developing under high density could cause individuals to invest more in RHP-related traits because these conditions might signal intense competition for mates in the near future. However, individuals reared under high density are often less aggressive than their low-density counterparts. The food available to an adult could also be important because the consumption of fat could improve an individual’s stamina, an RHP-related trait important in combat. Our study testing the impact of these two factors on male fighting ability in the sand field cricket (Gryllus firmus) found limited support for the hypothesis that rearing density and diet significantly influence a male’s ability to win a fight against another male. Instead we found stronger support for the notion that, all else being equal, males with larger mandibles, or weapons, than their opponent were more likely to win a fight.

VIS3COS

We study the impact of local density and stellar mass on the structure and morphology of approximately 500 quiescent and star-forming galaxies from the VIMOS Spectroscopic Survey of a Superstructure in COSMOS (VIS3COS). We perform bulge-to-disc decomposition of the surface brightness profiles and find ∼41 ± 3% of &gt; 1010 M⊙ galaxies to be best fitted with two components. We complement our analysis with non-parametric morphological measurements and qualitative visual classifications. We find that both galaxy structure and morphology depend on stellar mass and environment for our sample as a whole. We only find an impact of the environment on galaxy size for galaxies more massive than 1011 M⊙. We find higher Sérsic indices (n) and bulge-to-total ratios (B/T) in high-density regions when compared to low-density counterparts at similar stellar masses. We also find that galaxies with higher stellar mass have steeper light profiles (high n, B/T) compared to galaxies with lower stellar mass. Using visual classifications, we find a morphology–density relation at z ∼ 0.84 for galaxies more massive than 1010 M⊙, with elliptical galaxies being dominant at high-density regions and disc galaxies more common in low-density regions. However, when splitting the sample into colour–colour-selected star-forming and quiescent sub-populations, there are no statistically significant differences between low- and high-density regions. We find that quiescent galaxies are smaller, have higher Sérsic indices (for single profiles, around n ∼ 4), and higher bulge-to-total light ratios (for decomposed profiles, around B/T ∼ 0.5) when compared to star-forming counterparts (n ∼ 1 and B/T ∼ 0.3, for single and double profiles, respectively). We confirm these trends with non-parametric quantities, finding quiescent galaxies to be smoother (lower asymmetry, lower M20) and to have most of their light over smaller areas (higher concentration and Gini coefficient) than star-forming galaxies. Overall, we find a stronger dependence of structure and morphology on stellar mass than on local density and these relations are strongly correlated with the quenching fraction. The change in average structure or morphology corresponds to a change in the relative fractions of blue disc-like galaxies and red elliptical galaxies with stellar mass and environment. We hypothesise that the processes responsible for the quenching of star formation must also affect the galaxy morphology on similar timescales.

Oxidation behaviour of plasma-sprayed ZrB2-SiC coatings

Current study aimed at investigating oxidation behaviour of plasma-sprayed ZrB2-SiC coatings, which were deposited using different spray powers. Moreover, oxidation tests were carried out within temperature range of 400–1200 °C. Results from X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS) suggested that ZrB2-SiC coatings had been markedly oxidized at 600 °C. Besides, oxidation behaviour of ZrB2-SiC block ceramics, which had achieved different densities using spark plasma sintering (SPS) and pressureless sintering (PS), was also studied to explain oxidation behaviour of plasma-sprayed ZrB2-SiC coatings. Results revealed that high-density ZrB2-SiC block ceramics displayed better oxidation resistance than low-density counterparts, indicating that unfavorable oxidation resistance of ZrB2-SiC coatings could be ascribed to low density, since there were more pores in ZrB2-SiC coatings, which provided channels for oxygen diffusion.

Engineering of a hybrid nanoparticle-based nicotine nanovaccine as a next-generation immunotherapeutic strategy against nicotine addiction: A focus on hapten density

Although vaccination is a promising way to combat nicotine addiction, most traditional hapten-protein conjugate nicotine vaccines only show limited efficacy due to their poor recognition and uptake by immune cells. This study aimed to develop a hybrid nanoparticle-based nicotine vaccine with improved efficacy. The focus was to study the impact of hapten density on the immunological efficacy of the proposed hybrid nanovaccine. It was shown that the nanovaccine nanoparticles were taken up by the dendritic cells more efficiently than the conjugate vaccine, regardless of the hapten density on the nanoparticles. At a similar hapten density, the nanovaccine induced a significantly stronger immune response against nicotine than the conjugate vaccine in mice. Moreover, the high- and medium-density nanovaccines resulted in significantly higher anti-nicotine antibody titers than their low-density counterpart. Specifically, the high-density nanovaccine exhibited better immunogenic efficacy, resulting in higher anti-nicotine antibody titers and lower anti-carrier protein antibody titers than the medium- and low-density versions. The high-density nanovaccine also had the best ability to retain nicotine in serum and to block nicotine from entering the brain. These results suggest that the hybrid nanoparticle-based nicotine vaccine can elicit strong immunogenicity by modulating the hapten density, thereby providing a promising next-generation immunotherapeutic strategy against nicotine addiction.

The effect of particle density on ultrasound-mediated transport of nanoparticles

A significant barrier to successful drug delivery is the limited penetration of nanoscale therapeutics beyond the vasculature. Building on recent in vivo findings in the context of cancer drug delivery, the current study investigates whether modification of nanoparticle drug-carriers to increase their density can be used to enhance their penetration into viscoelastic materials under ultrasound exposure. A computational model is first presented to predict the transport of identically sized nanoparticles of different densities in an ultrasonic field in the presence of an oscillating microbubble, by a combination of primary and secondary acoustic radiation forces, acoustic streaming and microstreaming. Experiments are then described in which near monodisperse (polydispersity index <0.2) nanoparticles of approximate mean diameter 200 nm and densities ranging from 1.01 g cm−3 to 5.58 g cm−3 were fabricated and delivered to a tissue-mimicking material in the presence or absence of a microbubble ultrasound contrast agent, at ultrasound frequencies of 0.5 MHz and 1.6 MHz and a peak negative pressure of 1 MPa. Both the theoretical and experimental results confirm that denser particles exhibit significantly greater ultrasound-mediated transport than their lower density counterparts, indicating that density is a key consideration in the design of nanoscale therapeutics.

Ultrasound-mediated transport of nanoparticles and the influence of particle density

A significant barrier to successful drug delivery in cancer therapy is the limited penetration of nanoscale therapeutics deep into tumors. Ultrasound mediated cavitation has been shown to promote nanoparticle transport, but achieving tumor wide distribution still represents a considerable challenge. The current study investigates the way in which nanoparticle drug-carriers may be designed to enhance penetration under ultrasound exposure. A computational model has been developed to predict the transport of a nanoparticle in an ultrasonic field in the presence of an oscillating microbubble, by a combination of primary and secondary acoustic radiation forces, acoustic streaming, and microstreaming. Experimental investigations were also performed in a tissue-mimicking phantom to study the transport of different types of particle, in the presence or absence of a microbubble ultrasound contrast agent, at ultrasound frequencies of 0.5 MHz and 1.6 MHz with peak pressures in the range of 0–2.0 MPa. Micro- and nanoparticles with contrasting density cores ranging from 1.0 g/cm3 to 19.3 g/cm3 were used for the study. Both the theoretical and experimental results showed that the denser particles exhibit significantly greater ultrasound-mediated transport than their lower density counterparts, indicating that this is a key consideration in the design of nanoscale therapeutics.

Zonal-Level Urban Sprawl Analysis using Digitally-Merged Resourcesat-LISS IV and Cartosat-PAN Bitemporal Data

Remote sensing and GIS along with collateral data help analyzing the growth, pattern and extent of urban sprawl. With such a spatial and temporal analyses, it is possible to identify the pattern of sprawl and subsequently predict the nature of future expansion. The article brings out the extent and spatial distribution of urban sprawl over a period of six years i.e. 2005-2011 using Resourcesat-1 LISS-IV and Cartosat-1 PAN data over Hyderabad metropolitan city, Telangana state, India. The approach comprises data preparation-radiometric normalization, geo-referencing and image fusion; on-screen visual interpretation, and change analysis in a GIS environment. The study reveals that the built-up land have expanded by 8.65% during the 6-year period. Furthermore, in terms of growth, the high density built-up land score over their low density counterpart (5.7% versus 2.96%). Such a growth could happen at the cost of scrubs, cropland and barren/rocky area to a great extent and at the expanse of water bodies to a lesser extent. An estimated 65.294 sqkm of scrubs, 40.319 sqkm of cropland and 14.523 sqkm of barren/rocky areas have been transformed into settlements. Data used, methodology employed and the results of the study are discussed in detail.

INCREASES IN SEED DENSITY CAN IMPROVE PLANT STAND AND INCREASE SEEDLING VIGOUR FROM SMALL SEEDS OF WHEAT (TRITICUM AESTIVUM)

SUMMARYEarly vigour in wheat (Triticum aestivum) is an important physiological trait to improve water-use efficiency and grain yield, especially on light soils in Mediterranean-type climates. Potential interactions for plant stand and seedling vigour between seed density and various seed quality treatments were examined for wheat grown in two experiments, conducted under controlled and field environments in Western Australia. Seed lots were graded into seed size classes and seed density fractions using saturated solutions of ammonium sulphate or sodium polytungstate. Dense seed improved plant stands or produced seedlings with greater early seedling vigour than their low-density counterparts in all three field environments. Artificial ageing reduced germination and emergence in the controlled environment. When grown in the field at Merredin, Western Australia, on the sandy soil, plant development was delayed with aged seed, and total leaf area and dry weight of plants were reduced. Fungicide application diminished total plant dry weight in sandy soils, but had a much larger detrimental effect when applied to aged and low-density seeds than normal seeds, retarding development, total leaf area and total plant dry weight. Our results indicate that an increase in seed density, particularly in small seed, can potentially improve plant stand and seedling vigour independently of seed size, and may be especially important for wheat grown on sandy soils of poor fertility and low water-holding capacity. The results also suggest consistency in seedling vigour may benefit from combined screening against small seed size and low seed density, which may also reduce the likelihood of adverse reactions to seed-applied fungicides. More attention should be paid to seed density as a valuable trait for improved reliability in plant stand and seedling vigour.

Comparative studies on lectin–carbohydrate interactions in low and high density homo- and heteroglycoclusters

A versatile synthetic procedure to construct series of high- and low-density homo- and heteroglycoclusters is reported. The binding properties of these synthetic multivalent glycoconjugates to concanavalin A (Con A), a model lectin, have been assessed by using a range of competitive and non-competitive binding assays including enzyme-linked lectin assays (ELLA), isothermal titration microcalorimetry (ITC) and surface plasmon resonance (SPR). In all cases, highly dense glycoclusters showed a substantial amplification of the lectin-binding strength in comparison with low-density counterparts. Interestingly, highly-dense glycoligand presentations, regardless of their homo- or heteroglycoligand pattern, furnished similar Con A binding properties, supporting the existence of a synergic effect (heterocluster effect) due to secondary interactions of "non-active" structural motifs in the presence of a certain density of "active" glycoligands.

Modular Design of Li-Ion and Li-Polymer Batteries for Undersea Environments

AbstractLi-Ion chemistry is ideal for undersea environments. The cells are sealed and do not outgas, and the polymer versions can withstand pressures greater than 10,000 psi. This combination results in a battery that is easier and safer to use and one that does not require heavy, expensive pressure vessels.Recent advances in electronic control of the Li-Ion battery and new modular design concepts for construction of complex battery systems have resulted in battery systems that are more robust, more flexible, longer lived, easier to charge and maintain, and safer than their lower density counterparts. These new Li-Ion battery systems can be designed to deliver this energy at high voltages and high currents. Electronic charge control within the battery system allows charging by direct connection to power supplies or constant power sources such as fuel cells and solar panels.The modular design concept for Li-Ion and Li-Polymer battery systems are presented with an emphasis on construction for undersea applications. Key to the modular battery system design concept is the ability to electronically balance all the cells within the battery system automatically without operator intervention. Two different methods are described, which show how electronic balancing of all the cells within the battery system is accomplished. Examples of production battery systems already in service are shown, and systems under development are provided.

THE ENVIRONMENTAL INFLUENCE ON THE EVOLUTION OF LOCAL GALAXIES

The results of an Hα photometric survey of 30 dwarf galaxies of various morphologies in the Centaurus A and Sculptor groups are presented. Of these 30, emission was detected in 13: eight are of late-type, two are early-type, and three are of mixed morphologies. The typical flux detection limit of ∼ 2 × 10 −16 erg s −1 cm −2 translates into a star-formation rate (SFR) detection limit of 4 × 10 −6 Myr −1 . In light of these results, the morphology-density relation is re-examined, and it is shown that, despite a number of unaccounted parameters, there are significant correlations between the factors determining the morphological type of a galaxy and its environment. Dwarf galaxies in high-density regions have a lower current SFR and lower neutral gas content than their low-density counterparts, confirming earlier results from the Local Group and other denser environments. The effect of environment is also seen in the timescale formed from the ratio of blue luminosity to current SFR—dwarfs in higher-density environments have larger values, indicating relatively higher past average SFR. The influence of environment extends very far, and no dwarfs from our sample can be identified as field objects.

Dietary supplementation of l-tryptophan mitigates crowding stress and augments the growth in Cirrhinus mrigala fingerlings

A 60 days feeding trial was conducted to study the stress mitigation and hence growth augmenting effect of dietary l-tryptophan during high density group stress in Cirrhinus mrigala fingerlings. Four hundred eighty fingerlings were distributed into eight experimental groups. Each group either of low density group (10 fishes/75 L water) or higher density group (30 fishes/75 L water) was fed with a diet containing either 0, 0.68, 1.36 or 2.72% l-tryptophan in the diet, thus eight experimental groups viz. low density control (LC) (basal feed + 0% l-tryptophan); LT1 (basalfeed + 0.68% l-tryptophan); LT2 (basalfeed + 1.36% l-tryptophan); LT3 (basalfeed + 2.72% l-tryptophan) high density control (HC) (basal feed + 0% l-tryptophan); HT1 (basalfeed + 0.68% l-tryptophan); HT2 (basalfeed + 1.36% l-tryptophan); and HT3 (basalfeed + 2.72% l-tryptophan) were fed at 3% of the body weight with isonitrogenous (34.33 ± 0.23 to 35.81 ± 0.18 CP%) and isocaloric (423.49 ± 1.76 to 425.85 ± 0.31 K.Cal/100 g) purified diets. The possible role of dietary l-tryptophan on stress mitigation was assessed in terms of blood glucose, plasma cortisol, lactate dehydrogenase (LDH), malate dehydrogenase (MDH), alanine amino transferase (ALT), aspartate amino transferase (AST), acetyl choline esterase (AChE) assays, whereas growth was evaluated in terms of weight gain %, specific growth (SGR) and protein efficiency ratio (PER). The LDH, MDH, ALT, AST activities were found to be significantly higher ( p < 0.05) in the control groups and decreasing trend of LDH, MDH, ALT and AST activities were observed with the increasing level of dietary l-tryptophan. However, high density group exhibited significantly higher value ( p < 0.05) for the above parameters than their low density counterpart at similar level of l-tryptophan in the diet. In contrast to above parameters, AChE activity exhibited a reverse trend. In both the stocking densities, l-tryptophan supplemented groups found to have higher ( p < 0.05) growth, SGR and PER. The Plasma cortisol level was found to be significantly higher in the high density group than its low density counterpart. However, gradual supplementation of l-tryptophan in diet significantly reduced the cortisol level both in high density ( Y = − 26.33 x + 219.53, r 2 = 0.95) and low density group ( Y = − 27.57 x + 169.28, r 2 = 0.92). Similar trend was also found in blood glucose. Hence, dietary supplementation of l-tryptophan at a minimum level of 1.36% concomitantly reduced the stress in C. mrigala fingerlings. Though 2.72% dietary tryptophan also reduces the stress but 1.36% level appears to be cost effective.