The street foods play an important socioeconomic role in meeting food and nutritional requirements of city consumers at affordable prices to the lower and middle income people. The number of food poisoning notifications rose steadily worldwide since the inception of E. coli O157:H7 outbreak in the 1980s to date. This may be partly attributed to improved surveillance, increased global trade and travel, changes in modern food production, the impact of modern lifestyles, changes in food consumption, and the emergence of new pathogens. Consumer's knowledge and attitude may influence food safety behavior and practice. For the sake of public health, it is important to understand the epidemiology of foodborne illnesses that help in prevention and control efforts, appropriately allocating resources to control foodborne illness, monitoring and evaluation of food safety measures, development of new food safety standards, and assessment of the cost-effectiveness of interventions. This review paper described the sociodemographic characteristics, common hazards, and occupational hazards of street food vendors, microbial risk associated with street food, food safety interventions and control measures, regulatory aspects and legal requirements, financial constraints, and attitudes.
A transverse computer-generated hologram (CGH) diffracts and provides flexible control of incident light by steering it to any point in the projected image plane -i.e.CGHs are able to direct the light to where it is needed and away from where it is not 1 .In addition, the number of resolvable points in the image projection plane is a function of the CGH's pixel count 2 . Here we report a longitudinal CGH (LCGH), a photonic structure, which swaps the ability to steer light toward fixed spatial points for digital control in the frequency domain. This is of particular interest in the context of tunable lasers. In this regard, an LCGH offers two important degrees-of-freedom (DOFs): 1) provides high-resolution wavevector or k-space resolution within the Brillouin zone; 2) enables full control to define or modify the reflectivity at each resolvable k-point, so attaining a target spectral response. We demonstrate the flexibility of our LCGH approach by achieving purely electronic tuning between six digitally-selected operating frequencies in a single-section terahertz (THz) quantum cascade laser (QCL) 3 . These switchable single-frequency devices will simplify combining the power and flexibility of (Fig. 1d) enabling switching between these modes, i.e.electronically-controlled discrete tuning.In order to understand the first DOF, consider an LCGH of 2N pixels in the form of a spatial relative permittivity distribution ε(z), where L = NΛ is the total length and Λ the 3 minimum hologram-element separation. There exists an approximate FT relationship between ε(z) and the spectral reflectivity response ρ(k)18-20 :Due to the pixelated nature of the spatial domain z, the wavevector k is unique only over the interval (0,k B ), with a maximum N number of resolvable k-points resulting in a density of states Δk = (k B /N)(n eff /n g ) 21, 22 , where k B = π/n eff Λ is the wavevector corresponding to the edge of Brillouin zone, n eff is the effective modal refractive index, n g is the group refractive index All QCLs were fabricated from a molecular beam epitaxially grown GaAs/Al 0.15 Ga 0.85 As wafer, V557, with an 11.4 µm-thick active region based on reference 25. V557 was processed (Fig. 2 caption) into SP waveguides and cleaved into ~6 mm-long Fabry-Perot (FP) cavities.All devices displayed similar performance characteristics − as a typical example Fig. 2a shows the FP spectra of device A, recorded at four driving current densities. As expected, In order to generate the real-space lattice structure (i.e. the LCGH) satisfying ρ target , we exploit equation 1. The pixelated nature of the real-space allows this design to be implemented using a discrete FT, specifically a fast Fourier transform (FFT). Identifying an "optimised" LCGH architecture is computationally non-trivial, particularly when N is large.An FFT-based simulated annealing (SA) inverse optimisation algorithm was chosen, details 5 of which, including the number of optimisation parameters, are described in references 26and 27. The choice of algorithm is not critica...
A holographically designed, aperiodic distributed feedback grating is used as a multi-resonance filter and embedded within an existing Fabry-Pérot (FP) terahertz (THz) quantum cascade laser (QCL) cavity. Balancing the feedback strengths of the filter resonances and the FP cavity creates a system capable of a high degree of single-mode selectivity, which is sensitive to changes in driving current. Multi-moded QCLs operating around 2.9 THz are thus modified to achieve purely electronic discrete tuning spanning over 160 GHz with an average tuning resolution of 30 GHz. Applying the same multi-resonance filter to QCLs with gain peaks around 2.65 and 2.9 THz leads to dual-mode lasing with an electrically controlled frequency separation of between 190 and 267 GHz. A phase sensitive mode selection mechanism is experimentally confirmed by the observation of divergent fine-tuning of the lasing modes.
Focussed ion beam milling can be used to introduce aperiodic distributed feedback (ADFB) gratings into fully packaged, operational terahertz quantum cascade lasers to achieve electronically controlled, discretely tunable laser emission. These aperiodic gratingsdesigned using computer-generated hologram techniques -consist of multiple slits in the surface plasmon waveguide, distributed along the length of the laser cavity. Tuning behaviour and output power in ADFB lasers operating around 2.9 THz are investigated with a variety of slit dimensions and grating scales. Mode selectivity and grating losses are found to be strongly dependent on milling depth into the upper waveguide layers, dramatically increasing as the metallic layers are penetrated, then rising more slowly with deeper milling into the laser active region. Grating scale and placement along the laser cavity length are also shown to influence mode selection.
We present a perturbative aperiodic distributed feedback grating embedded within a Fabry-Pérot cavity. Time domain modelling revealed electronic switching functionality, occurring only in the presence of facet reflections. The switching behaviour was experimentally verified.
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