Petroleum based thermoplastics are widely used in a range of applications, particularly in packaging. However, their usage has resulted in soaring pollutant emissions. Thus, researchers have been driven to seek environmentally friendly alternative packaging materials which are recyclable as well as biodegradable. Due to the excellent mechanical properties of natural fibres, they have been extensively used to reinforce biopolymers to produce biodegradable composites. A detailed understanding of the properties of such composite materials is vital for assessing their applicability to various products. The present review discusses several functional properties related to packaging applications in order to explore the potential of bamboo fibre fabric-poly (lactic) acid composites for packaging applications. Physical properties, heat deflection temperature, impact resistance, recyclability and biodegradability are important functional properties of packaging materials. In this review, we will also comprehensively discuss the chronological events and applications of natural fibre biopolymer composites.
Solid polymer electrolyte (SPE) composed of semi-crystalline poly (vinylidene fluoride-hexafluoropropylene) [P(VdF-HFP)] copolymer, 1-ethyl-3-methylimidazolium bis (trifluoromethyl sulphonyl) imide [EMI-BTI] and graphene oxide (GO) was prepared and its performance evaluated. The effects of GO nano-filler were investigated in terms of enhancement in ionic conductivity along with the electrochemical properties of its electrical double layer capacitors (EDLC). The GO-doped SPE shows improvement in ionic conductivity compared to the P(VdF-HFP)-[EMI-BTI] SPE system due to the existence of the abundant oxygen-containing functional group in GO that assists in the improvement of the ion mobility in the polymer matrix. The complexation of the materials in the SPE is confirmed in X-ray diffraction (XRD) and thermogravimetric analysis (TGA) studies. The electrochemical performance of EDLC fabricated with GO-doped SPE is examined using cyclic voltammetry and charge-discharge techniques. The maximum specific capacitance obtained is 29.6 F∙g(-1), which is observed at a scan rate of 3 mV/s in 6 wt % GO-doped, SPE-based EDLC. It also has excellent cyclic retention as it is able keep the performance of the EDLC at 94% even after 3000 cycles. These results suggest GO doped SPE plays a significant role in energy storage application.
MeSH terms: Electric Conductivity; Electrolytes; Graphite; Humans; Imidazoles; Imides; Oxygen; Patient Discharge; Polymers; Vinyl Compounds; X-Ray Diffraction; Electric Capacitance
Driven by the trends towards miniaturization in lead free electronic products, researchers are putting immense efforts to improve the properties and reliabilities of Sn based solders. Recently, much interest has been shown on low silver (Ag) content solder SAC105 (Sn-1.0Ag-0.5Cu) because of economic reasons and improvement of impact resistance as compared to SAC305 (Sn-3.0Ag-0.5Cu. The present work investigates the effect of minor aluminum (Al) addition (0.1-0.5 wt.%) to SAC105 on the interfacial structure between solder and copper substrate during reflow. The addition of minor Al promoted formation of small, equiaxed Cu-Al particle, which are identified as Cu₃Al₂. Cu₃Al₂ resided at the near surface/edges of the solder and exhibited higher hardness and modulus. Results show that the minor addition of Al does not alter the morphology of the interfacial intermetallic compounds, but they substantially suppress the growth of the interfacial Cu₆Sn₅ intermetallic compound (IMC) after reflow. During isothermal aging, minor alloying Al has reduced the thickness of interfacial Cu₆Sn₅ IMC but has no significant effect on the thickness of Cu₃Sn. It is suggested that of atoms of Al exert their influence by hindering the flow of reacting species at the interface.
A search for narrow resonances decaying to an electron and a muon is presented. The [Formula: see text] [Formula: see text] mass spectrum is also investigated for non-resonant contributions from the production of quantum black holes (QBHs). The analysis is performed using data corresponding to an integrated luminosity of 19.7[Formula: see text] collected in proton-proton collisions at a centre-of-mass energy of 8[Formula: see text] with the CMS detector at the LHC. With no evidence for physics beyond the standard model in the invariant mass spectrum of selected [Formula: see text] pairs, upper limits are set at 95 [Formula: see text] confidence level on the product of cross section and branching fraction for signals arising in theories with charged lepton flavour violation. In the search for narrow resonances, the resonant production of a [Formula: see text] sneutrino in R-parity violating supersymmetry is considered. The [Formula: see text] sneutrino is excluded for masses below 1.28[Formula: see text] for couplings [Formula: see text], and below 2.30[Formula: see text] for [Formula: see text] and [Formula: see text]. These are the most stringent limits to date from direct searches at high-energy colliders. In addition, the resonance searches are interpreted in terms of a model with heavy partners of the [Formula: see text] boson and the photon. In a framework of TeV-scale quantum gravity based on a renormalization of Newton's constant, the search for non-resonant contributions to the [Formula: see text] [Formula: see text] mass spectrum excludes QBH production below a threshold mass [Formula: see text] of 1.99[Formula: see text]. In models that invoke extra dimensions, the bounds range from 2.36[Formula: see text] for one extra dimension to 3.63[Formula: see text] for six extra dimensions. This is the first search for QBHs decaying into the [Formula: see text] [Formula: see text] final state.
Introduction The risk factors associated with mental health among adolescents are usually
described by researchers at an individual level. Neighbourhood factors and
health have opened a new insight into the field of epidemiology. The aim of
this study was to assess the reliability and validity of a newly developed
Neighbourhood Factors on Mental Health Questionnaire among Malaysian
adolescents.
Methods A cross-sectional study was conducted in four secondary schools in Kuala
Lumpur, Malaysia using a newly developed questionnaire which comprised
of two main domains and seven items. Exploratory factor analysis and
Cronbach‟s alpha were used to measure the instrument‟s construct validity
and reliability.
Results A total of 106 adolescents participated in this research. The majority of
adolescents were 13 years old (40.6%), female (55.7%), Malays (68.9%),
have parents who only studied until secondary school (66.0%) and lived in
flats (32.1%). Bartlett‟s Test of Sphericity was significant (Chi-square =
258.361, p
Air pollution has been widely known to have an influence on health of the general population.
Air pollution can result from natural causes, human activities and transboundary air pollution.
Weather and climate play crucial role in determining the pattern of air quality. In recent years,
air pollution and recurrent episodes of haze has become a major concern in Malaysia.
Surveillance data on concentrations of main air pollutants such as carbon dioxide, (CO2),
Nitrogen Dioxide (NO2), Ozone (O3), sulphur dioxide (SO2) and particulate matter (PM10)
were found to be higher during the haze days and this may have an impact on health of the
community as reflected by an increase in hospital admissions particularly the respiratory and
cardiovascular diseases.
MeSH terms: Air Pollutants; Air Pollution; Carbon Dioxide; Cardiovascular Diseases; Climate; Humans; Human Activities; Malaysia; Nitrogen Dioxide; Ozone; Sulfur Dioxide; Weather; Particulate Matter
Introduction Prolonged mechanical ventilation among cardiac surgery patient has been
found to be correlated with negative clinical outcome and increased
healthcare resources utilization. Prolonged mechanical ventilation (PMV)
was defined as the accumulative duration of 24 hours or more of
postoperative endotracheal intubation starting from transfer of the patient to
cardiac ICU. This study is aimed to identify the risk factors preoperative,
intra operative and postoperative for prolonged ventilation among cardiac
patients in AL-Thawra Modern General Hospital (TMGH).
Methods Observational study design was conducted during a two-month period (from
1 August 2014 to 30 September 2014). It was among 70 patients who were
admitted to cardiac surgery intensive care unit in Al-Thawra Modern General
Hospital and selected by convenient sampling. The soci-demographic
characteristic and clinical patient data were collected using short
questionnaire developed by researcher. All patients had the same anesthetic
and postoperative management. Statistical analysis was performed with SPSS
version 20 and using bivariate analysis and multivariate logistic regression.
The p-value of < 0.05 was found to be statistically significant.
Results Incidence of prolonged mechanical ventilator post cardiac surgery was 37.1%
(26/70) through bivariate analysis, multivariate logistic regression. Low
Ejection fraction of Left Ventricle was inversely related to mechanical
ventilation time (AOR= 0.872) with 95% confidence interval [0.790 - 0.963],
hemodynamic instability were associated with prolonged mechanical
ventilation time (AOR=16.35) with 95% confidence interval [2.558 -
104.556].
Conclusion Low ejection fraction of Left Ventricle and Hemodynamic Instability post
operation were identified risk factors for prolonged mechanical ventilation
post cardiac surgery.
Introduction During haze, at what level should Air Pollutant Index (API) showed, public
or private school be closed is not without controversy and is very much
debated. Therefore, the aim of this paper is to objectively quantify the
potential inhaled dose of PM10 associated with exposure at school and home
microenvironments during haze. The result of the health risk assessment will
be used to propose the API level for closing the school during haze episode.
Methods A hypothetical haze exposure scenario was created using the breakpoints of
PM10 concentration for calculation of API and respective inhaled dose during
haze. To determine the potential inhaled dose, we have considered many
factors that include time spent for specific physical intensity at school and
home microenvironments, age-specific and physical intensity-specific
inhalation rate (m3/min), and the indoor/outdoor ratio of PM10. To calculate
risk quotient (RQ), the inhaled dose was compared with the health reference
dose computed based on the concentration of PM10 in the Malaysian
Ambient Air Quality Standard.
Results When considering the specific exposure at each microenvironment (school
and home), the potential inhaled dose of PM10 was substantially lower when
school is closed for both primary and secondary school. The calculated risk
quotient (RQ) indicates that primary school children are likely to be affected
at slightly lower PM10 concentration (equivalent to API of 197) as compared
to secondary school children. Short duration of high physical activity
intensity during school breaks has contributed to a large proportion of inhaled
dose among school children indicating the important to avoid physical
activities during haze.
Conclusion Based on the assessment, taking into account the uncertainty of risk
assessment methodology, we proposed school to be closed when API reach
190 for both primary and secondary schools. These findings and
recommendations are only valid for naturally ventilated school and applicable
in the context of the current API calculation system and the existing
Recommended Air Quality Guideline values in Malaysia.
MeSH terms: Air Pollutants; Air Pollution; Child; Humans; Malaysia; Schools; Exercise; Risk Assessment; Uncertainty
Introduction The prevalence of Type 2 diabetes mellitus (T2DM) is increasing worldwide
and many of these affected individuals remain unidentified. Undiagnosed
T2DM may impose substantial public health implications because these
individuals remain untreated and at risk for complications. The objective of
this study was to determine the national prevalence of undiagnosed T2DM
and to identify the associated risk factors.
Methods A nationwide cross-sectional study was conducted involving 17,783
respondents. Two-stage stratified sampling design was used to select a
representative sample of the Malaysian adult population. Structured
validated questionnaires with face to face interviews were used to obtain
data. Respondents, who claimed that they were not having diabetes, were
then asked to perform a fasting blood glucose finger-prick test by Accutrend
GC machine.
Results The prevalence of undiagnosed T2DM was 8.9% (n=1587). The highest
percentage of undiagnosed T2DM was found among males (10.2%), 55-59
years old (13.4%), highest education attainers of primary school (11.1%),
Indians (10.3%), married (10.3%), working (8.9%) and living in the urban
areas (9.2%). Multivariate analyses showed that factors associated with
undiagnosed T2DM were gender, age group, ethnicity, marital status, obesity
and hypertension.
Conclusion This study found an increasing trend of undiagnosed T2DM in Malaysia
compared to 2006. This finding is alarming as risk factors associated with
undiagnosed diabetes were related to most of the socio-demographic factors
studied. Therefore, early diabetic screening is crucial especially among adults
aged 30 and above to prevent more serious complications of this disease.
MeSH terms: Adult; Blood Glucose; Cross-Sectional Studies; Diabetes Mellitus, Type 2; Fasting; Humans; Hypertension; Malaysia; Male; Marriage; Obesity; Public Health; Surveys and Questionnaires; Risk Factors; Prevalence; Multivariate Analysis; Marital Status
Introduction Physical activity assessment in children is the first step in assessing the
relationship between activity and health, as well as the determinants of
childhood physical activity and changes in activity level.Physical Activity
Questionnaire for Older Children (PAQ-C) is self- administered
questionnaire to assess physical activity among older children. The objective
of this study was to determine the validity and reliability of Physical Activity
Questionnaire for Older Children in Malay language PAQ-C (M).
Methods The validation study was done among 73 students aged 10 to 17 years old.
The PAQ-C was translated into Malay language using forward and backward
translation. The evaluation of the psychometric properties included internal
consistency, test-retest reliability and criterion validity. Reliability of PAQ-C
(M) was determined using Cronbach alpha and intra-class correlation
coefficient (ICC). The PAQ-C (M) was administered twice in one week
interval to assess test-retest reliability. Criterion validity was assessed
between PAQ-C (M) and 3 Day Physical Activity Recall (3DPAR).
Results The internal consistency of PAQ-C (M) assessment calculated in this study
was α = 0.75 and α = 0.77 for assessments one and two, respectively. The
ICC between individual items of PAQ-C (M) was 0.59 to 0.91, indicating
moderate to good correlation. The Spearmen correlation coefficient between
PAQ-C (M) and 3DPARwas acceptable (r=0.60, p
Introduction Overweight and obesity is a major public health problem in Malaysia. This study aims to determine the prevalence of overweight and obesity among the Malaysian adult population and their association with socio-demographic characteristics (gender, ethnic, and age groups).
Methods A total of 17,257 adults aged 18 years and older (8,252 men, 9,005 women)
were assessed for BMI status, with a response rate of 97.8%, through a household survey from the National Health and Morbidity Survey (NHMS), conducted in all states of Malaysia in 2011.
Results All socio-demographic factors were consistently associated with higher chance of being overweight (except gender and location) and obesity (except location and household income). The identified risk of overweight were
Indian (aOR: 1.8, 95% CI: 1.2-2.8), aged 50-59 years (aOR: 2.8, 95% CI: 2.0-3.9), widower (aOR: 1.6, 95% CI: 1.3-2.0), subject with secondary education (aOR: 1.2, 95% CI: 1.0-1.4), Homemaker/unpaid worker (aOR:
1.3, 95% CI: 1.1-1.4), and with high household income group (aOR: 1.3, 95% CI: 1.2-1.6). The identified risk of obesity were women (aOR: 1.4, 95% CI: 1.2-1.6), Indian (aOR: 1.7, 95% CI: 0.9-3.2), aged 30-39 years (aOR: 3.6,
95% CI: 2.4-5.5), widower (aOR: 1.2, 95% CI: 0.9-1.6), subjects with primary education (aOR: 1.2, 95% CI: 0.9-1.6), Homemaker/unpaid worker (aOR: 1.3, 95% CI: 1.1-1.6), and with middle household income group (aOR: 1.3, 95% CI: 1.2-1.6).
Conclusions Our data indicate a high prevalence of overweight and obesity in the
population. Several sociodemographic characteristics are associated with both overweight and obesity. This study highlights the serious problem ofoverweight and obesity among Malaysia adults. Documentation of these problems may lead to research and policy agendas that will contribute both to our understanding and to the reduction of these problems.
Study name: National Health and Morbidity Survey (NHMS-2011)
MeSH terms: Adult; Documentation; Female; Health Surveys; Humans; Malaysia; Male; Morbidity; Obesity; Public Health; Body Mass Index; Prevalence; Widowhood; Overweight
Skeletal degeneration due to aging, also known as osteoporosis, is a major health problem worldwide. Certain dietary components confer protection to our skeletal system against osteoporosis. Consumption of olives, olive oil and olive polyphenols has been shown to improve bone health. This review aims to summarize the current evidence from cellular, animal and human studies on the skeletal protective effects of olives, olive oil and olive polyphenols. Animal studies showed that supplementation of olives, olive oil or olive polyphenols could improve skeletal health assessed via bone mineral density, bone biomechanical strength and bone turnover markers in ovariectomized rats, especially those with inflammation. The beneficial effects of olive oil and olive polyphenols could be attributed to their ability to reduce oxidative stress and inflammation. However, variations in the bone protective, antioxidant and anti-inflammatory effects between studies were noted. Cellular studies demonstrated that olive polyphenols enhanced proliferation of pre-osteoblasts, differentiation of osteoblasts and decreased the formation of osteoclast-like cells. However, the exact molecular pathways for its bone health promoting effects are yet to be clearly elucidated. Human studies revealed that daily consumption of olive oil could prevent the decline in bone mineral density and improve bone turnover markers. As a conclusion, olives, olive oil and its polyphenols are potential dietary interventions to prevent osteoporosis among the elderly.
Numerous lines of evidence support that bone marrow is a rich source of stem cells that can be used for research purposes and to treat some complex blood diseases and cancers. Stem cells are a potential source for regenerative medicine and tissue replacement after injury or disease, and mother cells that possess the capacity to become any type of cell in the body. They are cells without specific structure and characterized by their ability to self-renew or multiply while maintaining the potential to develop into other types of cells. Stem cells can normally become cells of the blood, heart, bones, skin, muscles or brain. Although, there are different sources of stem cells, all types of stem cells have the same capacity to develop into multiple types of cells. Stem cells are generally described as unspecialized cells with unlimited proliferation capacity that can divide (through mitosis) to produce more stem cells. Several types of adult stem cells have been characterized and can be cultured in vitro, including neural stem cells, hematopoietic stem cells, mesenchymal stem cells, cardiac stem cells and epithelial stem cells. They are valuable as research tools and might, in the future, be used to treat a wide range of diseases such as hematological hereditary diseases, Parkinson's disease, diabetes mellitus, heart disease and many other diseases. Currently, two types of stem cells have been identified based on their origins, namely embryonic stem cells and adult stem cells. Collectively, although many kinds of literature have been studying stem cell application in terms of clinical practice, stem cell-based therapy is still in its infancy stage.
Antibiotic resistance has become a major public health problem throughout the world. The presence of antibiotic-resistant bacteria such as Staphylococcus aureus and antibiotic resistance genes (ARGs) in hospital wastewater is a cause for great concern today. In this study, 276 Staph. aureus isolates were recovered from hospital wastewater samples in Malaysia. All of the isolates were screened for susceptibility to nine different classes of antibiotics: ampicillin, ciprofloxacin, gentamicin, kanamycin, erythromycin, vancomycin, trimethoprim and sulfamethoxazole, chloramphenicol, tetracycline and nalidixic acid. Screening tests showed that 100 % of Staph.aureus isolates exhibited resistance against kanamycin, vancomycin, trimethoprim and sulfamethoxazole and nalidixic acid. Additionally, 91, 87, 50, 43, 11 and 8.7 % of isolates showed resistance against erythromycin, gentamicin, ciprofloxacin, ampicillin, chloramphenicol and tetracycline, respectively. Based on these results, 100 % of isolates demonstrated multidrug-resistant (MDR) characteristics, displaying resistance against more than three classes of antibiotics. Of 276 isolates, nine exhibited resistance to more than nine classes of tested antibiotics; these were selected for antibiotic susceptibility testing and examined for the presence of conserved ARGs. Interestingly, a high percentage of the selected MDR Staph.aureus isolates did not contain conserved ARGs. These results indicate that non-conserved MDR gene elements may have already spread into the environment in the tropics of Southeast Asia, and unique resistance mechanisms against several antibiotics may have evolved due to stable, moderate temperatures that support growth of bacteria throughout the year.
Poly (lactic) acid (PLA) composites have made their way into various applications that may require thermoforming to produce 3D shapes. Wrinkles are common in many forming processes and identification of the forming parameters to prevent them in the useful part of the mechanical component is a key consideration. Better prediction of such defects helps to significantly reduce the time required for a tooling design process. The purpose of the experiment discussed here is to investigate the effects of different test parameters on the occurrence of deformations during sheet forming of double curvature shapes with bamboo fabric reinforced-PLA composites. The results demonstrated that the domes formed using hot tooling conditions were better in quality than those formed using cold tooling conditions. Wrinkles were more profound in the warp direction of the composite domes compared to the weft direction. Grid Strain Analysis (GSA) identifies the regions of severe deformation and provides useful information regarding the optimisation of processing parameters.
Halloysite (HNT) is treated with sulfuric acid and the physico-chemical properties of its morphology, surface activity, physical and chemical properties have been investigated when HNT is exposed to sulfuric acid with treatment periods of 1 h (H1), 3 h (H3), 8 h (H8), and 21 h (H21). The significance of this and similar work lies in the importance of using HNT as a functional material in nanocomposites. The chemical structure was characterized by Fourier transform infrared spectroscopy (FTIR). The spectrum demonstrates that the hydroxyl groups were active for grafting modification using sulfuric acid, promoting a promising potential use for halloysite in ceramic applications as filler for novel clay-polymer nanocomposites. From the X-ray diffraction (XRD) spectrum, it can be seen that the sulfuric acid breaks down the HNT crystal structure and alters it into amorphous silica. In addition, the FESEM images reveal that the sulfuric acid treatment dissolves the AlO₆ octahedral layers and induces the disintegration of SiO₄ tetrahedral layers, resulting in porous nanorods. The Bruncher-Emmett-Teller (BET) surface area and total pore volume of HNTs showed an increase. The reaction of the acid with both the outer and inner surfaces of the nanotubes causes the AlO₆ octahedral layers to dissolve, which leads to the breakdown and collapse of the tetrahedral layers of SiO₄. The multi-fold results presented in this paper serve as a guide for further HNT functional treatment for producing new and advanced nanocomposites.
In this study microcrystalline cellulose (MCC) was oxidized by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation. The treated cellulose slurry was mechanically homogenized to form a transparent dispersion which consisted of individual cellulose nanofibers with uniform widths of 3-4 nm. Bio-nanocomposite films were then prepared from a polyvinyl alcohol (PVA)-chitosan (CS) polymeric blend with different TEMPO-oxidized cellulose nanofiber (TOCN) contents (0, 0.5, 1.0 and 1.5 wt %) via the solution casting method. The characterizations of pure PVA/CS and PVA/CS/TOCN films were performed in terms of field emission scanning electron microscopy (FESEM), tensile tests, thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The results from FESEM analysis justified that low loading levels of TOCNs were dispersed uniformly and homogeneously in the PVA-CS blend matrix. The tensile strength and thermal stability of the films were increased with the increased loading levels of TOCNs to a maximum level. The thermal study indicated a slight improvement of the thermal stability upon the reinforcement of TOCNs. As evidenced by the FTIR and XRD, PVA and CS were considered miscible and compatible owing to hydrogen bonding interaction. These analyses also revealed the good dispersion of TOCNs within the PVA/CS polymer matrix. The improved properties due to the reinforcement of TOCNs can be highly beneficial in numerous applications.
Waste water treatment reservoirs are contaminated with many hazardous chemicals and acids. Reservoirs typically comprise concrete and reinforcement steel bars, and the main elements responsible for their deterioration are hazardous chemicals, acids, and ozone. Currently, a variety of techniques are being used to protect reservoirs from exposure to these elements. The most widely used techniques are stainless steel plating and polymeric coating. In this study, a technique known as arc thermal spraying was used. It is a more convenient and economical method for protecting both concrete and reinforcement steel bar from deterioration in waste water treatment reservoirs. In this study, 316L stainless steel coating was applied to a concrete surface, and different electrochemical experiments were performed to evaluate the performance of coatings in different acidic pH solutions. The coating generated from the arc thermal spraying process significantly protected the concrete surface from corrosion in acidic pH solutions, owing to the formation of a double layer capacitance-a mixture of Cr3+ enriched with Cr₂O₃ and Cr-hydroxide in inner and Fe3+ oxide on the outer layer of the coating. The formation of this passive film is defective owing to the non-homogeneous 316L stainless steel coating surface. In the pH 5 solution, the growth of a passive film is adequate due to the presence of un-dissociated water molecules in the aqueous sulfuric acid solution. The coated surface is sealed with alkyl epoxide, which acts as a barrier against the penetration of acidic solutions. This coating exhibits higher impedance values among the three studied acidic pH solutions.
MeSH terms: Corrosion; Epoxy Compounds; Hydrogen-Ion Concentration; Hydroxides; Ozone; Stainless Steel; Steel; Sulfuric Acids; Water; Hazardous Substances; Electric Impedance; Water Purification; Waste Water
The aim of this paper is to introduce a compact double-negative (DNG) metamaterial that exhibits a negative refractive index (NRI) bandwidth of more than 3.6 GHz considering the frequency from 2 to 14 GHz. In this framework, two arms of the designed unit cell are split in a way that forms a Modified-Z-shape structure of the FR-4 substrate material. The finite integration technique (FIT)-based Computer Simulation Technology (CST) Microwave Studio is applied for computation, and the experimental setup for measuring the performance is performed inside two waveguide ports. Therefore, the measured data complies well with the simulated data of the unit cell at 0-degree and 90-degree rotation angles. The designed unit cell shows a negative refractive index from 3.482 to 7.096 GHz (bandwidth of 3.61 GHz), 7.876 to 10.047 GHz (bandwidth of 2.171 GHz), and 11.594 to 14 GHz (bandwidth of 2.406 GHz) in the microwave spectra. The design also exhibits almost the same wide negative refractive index bandwidth in the major region of the C-band and X-band if it is rotated 90 degrees. However, the novelty of the proposed structure lies in its effective medium ratio of more than 4, wide bandwidth, and compact size.
This work investigates the structural formation and analyses of titania membranes (TM) prepared using different vacuum exposure times for molecular weight (MW) cut-off performance and oil/water separation. Titania membranes were synthesized via a sol-gel method and coated on macroporous alumina tubes followed by exposure to a vacuum between 30 and 1200 s and then calcined at 400 °C. X-ray diffraction and nitrogen adsorption analyses showed that the crystallite size and particle size of titania increased as a function of vacuum time. All the TM membranes were mesoporous with an average pore diameter of ~3.6 nm with an anatase crystal morphology. Water, glucose, sucrose, and polyvinylpyrrolidone with 40 and 360 kDa (PVP-40 kDa and PVP-360 kDa) were used as feed solutions for MW cut-off and hexadecane solution for oil filtration investigation. The TM membranes were not able to separate glucose and sucrose, thus indicating the membrane pore sizes are larger than the kinetic diameter of sucrose of 0.9 nm, irrespective of vacuum exposure time. They also showed only moderate rejection (20%) of the smaller PVP-40 kDa, however, all the membranes were able to obtain an excellent rejection of near 100% for the larger PVP-360 kDa molecule. Furthermore, the TM membranes were tested for the separation of oil emulsions with a high concentration of oil (3000 ppm), reaching high oil rejections of more than 90% of oil. In general, the water fluxes increased with the vacuum exposure time indicating a pore structural tailoring effect. It is therefore proposed that a mechanism of pore size tailoring was formed by an interconnected network of Ti-O-Ti nanoparticles with inter-particle voids, which increased as TiO₂ nanoparticle size increased as a function of vacuum exposure time, and thus reduced the water transport resistance through the TM membranes.