Effect of External Debt on Economic Growth of Nigeria

The study examines the effect of external debt on the economic growth of Nigeria. The model built for the study proxy gross domestic product as the endogenous variable measuring economic growth as a function of external debt, ratio of external debt to export, inflation, and exchange rate proxy as the exogenous variables. Annual time series data was gathered from the Central Bank of Nigeria Statistical bulletin and Debt Management Office from 1970 to 2010. The econometric techniques of Ordinary Least Square(OLS), Augmented Dickey-Fuller (ADF) Unit Root test, Johansen Co-integration test and Error Correction Method (ECM) are employed in the empirical analysis. The co-integration test shows that long-run equilibrium relationship exist among the variables. The findings from the error correction method show that external debt has contributed positively to the Nigerian economy. The study recommends that government should ensure economic and political stability and external debt should be acquired largely for economic reasons rather than social or political reasons. Keywords: External Debt, Economic Growth, Gross Domestic Product, Error Correction Method

Levels of Heavy Metals in Soil, Water and Vegetables around Industrial area in Bauchi, Northeastern Nigeria

This study examined the levels of heavy metals in soil, water, and vegetables (amaranthus, hibiscussabdariffa, and allium cepa leaves) around the industrial area Bauchi, Northeastern Nigeria. The composite samples of soil, water, and vegetables were collected and determine the level of heavy metals (Mn, Zn, Cd, Pb, and As) using Atomic Absorption Spectrophotometer (AAS). The level of the heavy metals decreased in the order of Mn > Zn > Pb > Cd, Pb > Zn > Mn > Cd, and Mn > Zn > Mn > Cd in the soil, water, and vegetables respectively. Among the vegetables, amaranthus had the highest heavy metals level followed by allium cepa leaves and hibiscus sabdariffa. The levels of heavy metals obtained were below the tolerance level recommended by the world health organization (WHO). The bio-concentration factors of the heavy metals for the studied samples were below one except Zn in amaranthus. The daily intake of metals for Mn was found to be the highest in amaranthus for children and estimated to be 1.149 mg/person/day. Health risk index of Zn for amaranthus and allium cepa leaves for children and Pb for amaranthus, hibiscus sabdariffa and allium cepa leaves for both children and adults were above 1, except in hibiscus sabdariffa for adults, signifying provable of health risks for the consumption of the vegetables in the study area. Therefore, the consumption of these vegetables as food could pose a health hazard, and regular monitoring is recommended to prevent metal accumulation with their associated health implications in the consuming public

Prevalence and Outcome of Increased Nuchal Translucency in Usmanu Danfodiyo University Teaching Hospital, Sokoto, Nigeria: A Cohort Study

Background: An important component of the first‑trimester scan is nuchal translucency thickness at 11 weeks to 13 weeks 6 days of gestation. A nuchal translucency ≥3.3 mm is a significant early pregnancy scan finding associated with Trisomies 13, 18, and 21 and congenital heart diseases. Aims: To determine the prevalence and outcome of increased fetal nuchal translucency among pregnant women. Subjects and Methods: A prospective cohort study at the Obstetrics and Gynaecology Department of Usmanu Danfodiyo University Teaching Hospital Sokoto. This was a prospective study of 265 consecutively recruited women in the first trimester of pregnancy who presented to antenatal clinics over a 20‑week period. An NT scan was conducted at 11 weeks to 13 weeks 6 days followed by an anomaly scan at 18–22 weeks. Patients were followed up to delivery and 6‑week post‑partum. The neonates were examined at delivery and at 6‑week postnatal life. Data entry and analysis was done with IBM SPSS version 20. The level of significance was set at less than 0.05. Frequency distribution; student t‑test and Chi‑squared test. Results: The 95th percentile NT was 3.3 mm and the prevalence of increased  NT above 3.3 mm was 3%. The mean maternal age of the participants was28.1 ± 5.1 years and the modal parity was Para 0. The most common anomalies associated with increased NT were ventricular septal defect and spina bifida. A congenital anomaly was significantly associated with increased NT (P <0.001). Conclusions: The prevalence of increased fetal nuchal translucency is relatively high in our environment and is associated with congenital fetal defects. Routine screening with first‑trimester ultrasound will help detect congenital anomalies early

Optimizing tapered microfiber sensor design and simulation

Refractive index sensors measure the evanescent field energy to sense various environmental parameters. Evanescent field-based sensors depend on the tapered area geometry which is one of the important factors for optimising the sensor performance as well as achieving better sensitivity and higher resolution. Tapering fabrication process needs to be controlled properly in order to achieve the optimal design. A two-dimensional model of the tapered sensor is proposed and simulated using Finite Element Analysis software, COMSOL Multiphysics. The light scattering phenomenon is visualized for taper and waist areas. The effects of the taper length, the waist length and the waist diameter have been explored in order to find the optimal geometries design. The model provides initial data to the designer to program and control the taper ration and the taper length the fabrication process in order to obtain the highest penetration depth at the highest resolution. The results show that the evanescent field is significantly high when the core diameter is close or below the wavelength. The output graph illustrates that when the tapering ratio decreases, more light propagate into the surrounding making the sensor more sensitive to the ambient changes. The simulation shows that the profile of the sensor can be fine-tuned by changing the tapering ratio of the waist and the length of the taper in order to obtain high performance, ultra-high-resolution evanescent field sensor

Compact and wide-band bismuth-based erbium-doped fibre amplifier based on two-stage and double-pass approaches

In this study, a wide-band erbium-doped fibre amplifier (EDFA) operating in both C- and L-band wavelength regions is demonstrated based on two-stage and double-pass approaches. The amplifier employs two pieces of 21 and 46 cm long bismuthbased EDFs (Bi-EDFs) optimised for C- and L-band operations, respectively, which are pumped by 1480 nm laser diode and its performances are investigated in both parallel and linear configurations. Wide-band operation is achieved in both configurations that covers from 1525 to 1620 nm. Compared with the linear Bi-EDFA, the parallel Bi-EDFA provides a higher attainable gain especially for small input signal. At input signal power of 230 dBm, the average gains of the parallel Bi-EDFA are obtained at approximately 20 dB with gain variation of +2.5 dB within the wavelength region from 1530 to 1605 nm. At the input signal power of 0 dBm, the average gains of approximately 10 dB with a gain variation of +2 dB within 1540 to 1620 nm region are obtained by both parallel and linear Bi-EDFAs. The noise figures for both configurations are maintained below 10 dB in the wavelength region from 1535 to 1620 nm. The noise figures are mainly because of spurious reflection in the cavity and high reflection of amplified spontaneous emission (ASE) from the end face

An adiabatic silica taper based on two sequential tapering routines

Microfiber-based devices have a great potential in many applications due to their extraordinary optical and mechanical properties. An adiabatic silica-based taper is required for most of the applications and thus, adiabaticity criterion has to be estimated and satisfied to avoid high optical loss emerging when taper’s profile is not controlled properly. This requires obtaining propagation constants via solving boundary condition problem at each position along the taper. Yet, this procedure involves intensive computational and time-consuming solving of complex Maxwell vector equations. This paper proposed an efficient method to model the taper profile, evaluate the adiabaticity and simulate it using Finite Element Analysis software. The model facilitates design phase and optimize fabrication process for any fiber-based device. A slow gradual radius reduction rates can guarantee adiabatic profiles with the expense of longer transition sections. In miniature devices, such as sensors and micro-resonators, transition regions are preferable to be as short as possible while the narrow waist is preferred to be long and uniform. To balance between short transition preference and low loss condition, we proposed a design based on two tapering sequential routines. The simulation results confirmed our design adiabaticity. From the optical spectrum of the fabricated taper, it is found that the loss is less than 1dBm and the spectrum is not distorted

Stable double spacing multiwavelength Brillouin-Erbium doped fiber laser based on highly nonlinear fiber

A double frequency spaced multiwavelength Brillouin-Erbium doped fiber laser (BEDFL) with figure-of-eight cavity have been successfully developed and tested. Double frequency spacing is achieved by using a piece of 2 km of highly nonlinear fiber (HNLF) as a gain medium. Figure-of-eight configuration removes the odd order Stokes signals via a four-port circulator. Fifteen Stokes channels are simultaneously generated with a spacing of 0.154 nm that is around 20 GHz, when the Brillouin pump and 980 nm pump powers are fixed at the optimized values of 6 dBm and 40 mW, respectively. Fourteen anti stoke channels are also obtained, which are generated through four wave mixing (FWM) process in the laser cavity. The output is smooth triangular comb. The BEFL can also be tuned from 1526.5 to 1567.5 nm

Flat-gain wide-band erbium doped fiber amplifier with hybrid gain medium

A new erbium-doped fiber amplifier (EDFA) is demonstrated using a combination of zirconia-based erbium-doped fiber (Zr-EDF) and silica-based Erbium-doped fiber (Si-EDF) as the gain medium. The EDFA comprises a 2 m long Zr-EDF and 9 m long Si-EDF optimized for C- and L-band operations, respectively, in a double-pass parallel configuration. A chirp fiber Bragg grating (CFBG) is used in both stages to ensure double propagation of the signal and thus to increase the attainable gain in both C- and L-band regions. At an input signal power of 0 dBm, a flat gain of 15 dB is achieved with a gain variation of less than 0.5 dB within a wide wavelength range from 1530 to 1605 nm. The corresponding noise figure varies from 6.2 to 10.8 dB within this wavelength region

All-fibre dual-wavelength thulium-doped fibre laser based on spatial filtering effect

We report a room-temperature all-fibre dual-wavelength thulium-doped fibre laser that operates around 1900 nm and uses a spatial mode-beating filter in a ring configuration. By pumping the gain medium with an 800 nm laser and controlling the phase mismatch at the splicing points of a thulium-doped fibre, the two output lines are obtained at 1844.8 and 1852.0 nm, with the corresponding signal-to-noise ratios of 30 and 21 dB. The threshold pump power is 109.3 mW. At the maximum pump power of 131.7 mW, the output powers are 0.297 and 0.038 mW for the 1844.8 and 1852.0 nm laser lines, respectively

Wideband and compact erbium-doped fiber amplifier using parallel double-pass configuration

In this article, a wide-band erbium doped fiber amplifier (EDFA) that operates in both C- and L-band wavelength regions is demonstrated. The amplifier employs two pieces of 1.5 m and 9 m-long erbium doped fibers (EDFs) optimized for C-band and L-band operations, respectively, in double-pass parallel configuration to achieve a wideband operation from 1530 to 1605 nm. The chirp fiber Bragg grating is used in both stages to allow a double propagation of signal and thus increases the attainable gain in both C- and L-band regions. At an input signal power of −30 dBm, a measured gain varies from 23 to 36 dB within a wide wavelength region from 1530 to 1605 nm. The corresponding noise figure varies from 5.6 to 8.2 dB within this wavelength region. The gain and noise figure of the proposed parallel configuration is much better when compared to that of a serial amplifier