Thermodynamics of nanocrystal-ligand binding through isothermal titration calorimetry.

Manipulations of nanocrystal (NC) surfaces have propelled the applications of colloidal NCs across various fields such as bioimaging, catalysis, electronics, and sensing applications. In this Feature Article, we discuss the surface chemistry of colloidal NCs, with an emphasis on semiconductor quantum dots, and the binding motifs for various ligands that coordinate NC surfaces. We present isothermal titration calorimetry (ITC) as a viable technique for studying the thermodynamics of the ligand association and exchange at NC surfaces by discussing its principles of operation and highlighting results obtained to date. We give an in-depth description of various thermodynamic models that can be used to interpret NC-ligand interactions as measured not only by ITC, but also by NMR, fluorescence quenching, and fluorescence anisotropy techniques. Understanding the complexity of NC surface-ligand interactions can provide a wide range of avenues to tune their properties for desired applications.

Prevalence and risk factors of childhood anemia in Nepal: A multilevel analysis.

INTRODUCTION: Anemia is a common problem in children particularly in developing countries and taking steps to tackle it is one of the major public health challenges for Nepal. The objective of this study is to investigate the prevalence of individual, household and community level determinants of childhood anemia in Nepal. METHODS: Data was taken from a nationally representative sample of 1,942 Nepalese children aged from 6-59 months. The Chi-square test was used to determine the bivariate relationship between the selected variables and childhood anemia and a multilevel logistic regression model with a random intercept at household and community level was used to identify important determinants of this kind of anemia. RESULTS: The results showed that 52.6% (95% CI: 49.8%-55.4%) of the children were anemic while 26.6% (95% CI: 24.0%-29.3%) of them were moderate to severe. The prevalence of overall anemia was higher among children aged less than 11 months as well as in underweight children, children of underweight, anemic and uneducated mothers and those in the terrain ecological regions. Multivariable analysis showed that children aged less than 11 months, who were underweight and had anemic mothers were more likely to have moderate or severe anemia. Children in the hilly ecological region were less likely to have it compared to mountain and terrain ecological regions. Children in middle-class families and children of mothers who completed secondary education were more likely to have anemia. CONCLUSION: Nepal is facing a serious public health problem due to the high prevalence of childhood anemia. This adverse situation occurs due to socio-demographic and geographical factors such as age, malnutrition status, mother's anemia status, socio-economic status and regional variations. Prevention of childhood anemia should be given top priority in Nepal and should be considered as a major public health intervention.

Phytochemical analysis of mite-infested tea leaves of Darjeeling Hills, India.

INTRODUCTION: Darjeeling tea of India is one of the most famous beverages globally. However, a large amount of tea crop is damaged every year by the attack of mites. OBJECTIVES: The study aimed to determine the changes in different pigments and biochemical components of tea leaves due to mite infestation. MATERIALS AND METHODS: We used UV-visible and Fourier-transform infrared (FTIR) spectroscopy simultaneously to understand the damages in pigment contents of the leaves of tea (Camellia sinensis (L.) Kuntze) due to attack of phytophagus mite, Oligonychus coffeae Nietner. Furthermore, chemical analysis of infested tea leaves was also performed to compare the nutrients of the plants, namely total phenol, protein and soluble sugar. RESULTS: The UV-visible study reveals severe reduction of the pigments such as chlorophyll (Chl), carotenoids and xanthophylls in the tea leaf due to mite infestation. The findings of the FTIR study, also shows variation in different physiochemical components in the leaf Chl. The sugar and protein content of the infested leaves have been reduced compared to uninfested ones. Results in the case of tea leaves plucked during first (March) and third (November) flushes show similar trends. CONCLUSION: The increase in phenolic and alcoholic components and decrease in Chl contents may affect the quality of Darjeeling tea. The extent of damages done by the pests measured here could aid the pest management in tea gardens.

A Negative Index Metamaterial-Inspired UWB Antenna with an Integration of Complementary SRR and CLS Unit Cells for Microwave Imaging Sensor Applications.

This paper presents a negative index metamaterial incorporated UWB antenna with an integration of complementary SRR (split-ring resonator) and CLS (capacitive loaded strip) unit cells for microwave imaging sensor applications. This metamaterial UWB antenna sensor consists of four unit cells along one axis, where each unit cell incorporates a complementary SRR and CLS pair. This integration enables a design layout that allows both a negative value of permittivity and a negative value of permeability simultaneous, resulting in a durable negative index to enhance the antenna sensor performance for microwave imaging sensor applications. The proposed MTM antenna sensor was designed and fabricated on an FR4 substrate having a thickness of 1.6 mm and a dielectric constant of 4.6. The electrical dimensions of this antenna sensor are 0.20 λ × 0.29 λ at a lower frequency of 3.1 GHz. This antenna sensor achieves a 131.5% bandwidth (VSWR < 2) covering the frequency bands from 3.1 GHz to more than 15 GHz with a maximum gain of 6.57 dBi. High fidelity factor and gain, smooth surface-current distribution and nearly omni-directional radiation patterns with low cross-polarization confirm that the proposed negative index UWB antenna is a promising entrant in the field of microwave imaging sensors.

A Miniaturized Antenna with Negative Index Metamaterial Based on Modified SRR and CLS Unit Cell for UWB Microwave Imaging Applications.

A miniaturized antenna employing a negative index metamaterial with modified split-ring resonator (SRR) and capacitance-loaded strip (CLS) unit cells is presented for Ultra wideband (UWB) microwave imaging applications. Four left-handed (LH) metamaterial (MTM) unit cells are located along one axis of the antenna as the radiating element. Each left-handed metamaterial unit cell combines a modified split-ring resonator (SRR) with a capacitance-loaded strip (CLS) to obtain a design architecture that simultaneously exhibits both negative permittivity and negative permeability, which ensures a stable negative refractive index to improve the antenna performance for microwave imaging. The antenna structure, with dimension of 16 × 21 × 1.6 mm³, is printed on a low dielectric FR4 material with a slotted ground plane and a microstrip feed. The measured reflection coefficient demonstrates that this antenna attains 114.5% bandwidth covering the frequency band of 3.4-12.5 GHz for a voltage standing wave ratio of less than 2 with a maximum gain of 5.16 dBi at 10.15 GHz. There is a stable harmony between the simulated and measured results that indicate improved nearly omni-directional radiation characteristics within the operational frequency band. The stable surface current distribution, negative refractive index characteristic, considerable gain and radiation properties make this proposed negative index metamaterial antenna optimal for UWB microwave imaging applications.

Microwave Imaging Sensor Using Compact Metamaterial UWB Antenna with a High Correlation Factor.

The design of a compact metamaterial ultra-wideband (UWB) antenna with a goal towards application in microwave imaging systems for detecting unwanted cells in human tissue, such as in cases of breast cancer, heart failure and brain stroke detection is proposed. This proposed UWB antenna is made of four metamaterial unit cells, where each cell is an integration of a modified split ring resonator (SRR), capacitive loaded strip (CLS) and wire, to attain a design layout that simultaneously exhibits both a negative magnetic permeability and a negative electrical permittivity. This design results in an astonishing negative refractive index that enables amplification of the radiated power of this reported antenna, and therefore, high antenna performance. A low-cost FR4 substrate material is used to design and print this reported antenna, and has the following characteristics: thickness of 1.6 mm, relative permeability of one, relative permittivity of 4.60 and loss tangent of 0.02. The overall antenna size is 19.36 mm × 27.72 mm × 1.6 mm where the electrical dimension is 0.20 λ × 0.28 λ × 0.016 λ at the 3.05 GHz lower frequency band. Voltage Standing Wave Ratio (VSWR) measurements have illustrated that this antenna exhibits an impedance bandwidth from 3.05 GHz to more than 15 GHz for VSWR < 2 with an average gain of 4.38 dBi throughout the operating frequency band. The simulations (both HFSS and computer simulation technology (CST)) and the measurements are in high agreement. A high correlation factor and the capability of detecting tumour simulants confirm that this reported UWB antenna can be used as an imaging sensor.