Performances Analysis of Novel Proposed Code for SAC-OCDMA System

The development of SAC-OCDMA system is based on the creation of new code structure. A novel proposed code structure is called ZFD that is based on the combination of various matrix creation methods and especially on the factorial function. This approach has not been exploited before in the OCDMA system. This novel code has its own advantage that represented in its possibility to generate code-words in flexible way by setting variable basic codes at fixed code weight. The performance of this proposed code is demonstrated via mathematical methods. It is represented by its optimal cross-correlation to avoid the multiple access interference (MAI). Consequently, the effects of the contributed noises using direct detection method have been considered. These noises are represented by shot noise and thermal noise. In addition, a system of three users was simulated with ZFD code under the C band (1530–1565 nm) for the upstream signal with different channel spacing (0.8, 1 and 1.2 nm). In this paper, several parameter effects such as fiber length, effective source power and data rate have been studied and compared to prove the effectiveness of this code. Also, ZFD code has been compared to some other codes such as RD, EDW and MDW according to the previous parameters. The suggested code has reached good results in terms of the bit error rate (BER) and the eye diagram.

High-Precision Light Spot Position Detection in Low SNR Condition Based on Quadrant Detector

In free space optical communications, long-distance transmission leads to the attenuation of beacon light, where we adopt a quadrant detector (QD) to receive the weak signal. However, the background light interferes so strongly that the output signal-to-noise ratio (SNR) of QD is at a low level, which causes a decrease in accuracy of the direct detection method. This requires finding a new light spot detection method, so an improved detection method is proposed. Because the dark current noise and the background light noise are both white noise, we adopt a Kalman filter to estimate the real output of four electric signals of QD. Unfortunately, running these through an amplifier introduces some direct current (DC) offsets into the signals. In order to balance the effect of the DC offsets, we consider using the modulation method, where we employ a sine signal to modulate the intensity of the beacon light at the transmitting end, after which we can give an inverse gain to move the center of signals to near zero to eliminate the DC offsets when we calculate the data. In Kalman filtering, we use the peak values of the signals in every period after the analog to digital converter (ADC) as the elements of the measurement matrix. Experimental results show that even when QD output SNR is about −10 dB, the detection root-mean-square errors decrease by 51.5% using the improved detection method compared with the direct detection method. Moreover, Kalman filtering does not require a large amount of data, which means it works efficiently, can reduce the cost of hardware resources, and is available for the real-time calculation of spot position.

A high-precision dynamic model of a sounding rocket and rapid wind compensation method research

Sounding rockets are the only direct detection method for near-space and are utilized for different kinds of scientific research. Dynamic models are the foundation of research on sounding rockets. However, no dynamic models have included all the working processes of a sounding rocket. A high-precision dynamic model of a sounding rocket is proposed in this article; the model includes motion on the launch rail, the free flight phase, parachute deployment, the inflation process, and steady descent. Through the model, the entirety of the dynamic process can be understood in detail to help improve performance. A combination wind compensation method was investigated to rapidly and accurately obtain launch parameters; the method was derived from a wind weighting and pattern search method. Based on the simulation results, the proposed approaches are proven to be effective.

Quantitative Identification of Adulterated Sichuan Pepper Powder by Near-Infrared Spectroscopy Coupled with Chemometrics

Sichuan pepper is a traditional and important flavoring of Chinese cuisine. It has attracted increasing interest in recent years owning to its unique taste and aroma. However, some cheap adulterants have been illegally found in Sichuan pepper powder in the market due to merchants trying to cut costs and gain an extra profit. In order to determine the compositions of Sichuan pepper powder quickly and effectively, a direct detection method using near-infrared (NIR) spectroscopy has been developed. 462 samples of adulterated Sichuan pepper powder mixed with different amounts of wheat bran, rice bran, corn flour, and rosin powder were studied. The NIR spectra data was studied using partial least squares (PLS) analysis. The method was found to be capable of predicting the compositions of adulterated Sichuan pepper powder. The determination coefficients of prediction set (Rp2) with the best pretreatments were 0.971 for Sichuan pepper powder, 0.948 for rice bran, 0.969 for wheat bran, 0.967 for corn flour, and 0.994 for rosin powder, respectively. The standard errors of prediction (SEP) were 2.81%, 2.38%, 3.19%, 2.46%, and 1.10%, respectively. The results showed that NIR spectroscopy with chemometrics is a rapid and nondestructive tool for the quantitative analysis of adulterated Sichuan pepper powder.

Single Molecule Investigation of Ag+ Interactions with Single Cytosine-, Methylcytosine- and Hydroxymethylcytosine-Cytosine Mismatches in a Nanopore

Both cytosine-Ag-cytosine interactions and cytosine modifications in a DNA duplex have attracted great interest for research. Cytosine (C) modifications such as methylcytosine (mC) and hydroxymethylcytosine (hmC) are associated with tumorigenesis. However, a method for directly discriminating C, mC and hmC bases without labeling, modification and amplification is still missing. Additionally, the nature of coordination of Ag+ with cytosine-cytosine (C-C) mismatches is not clearly understood. Utilizing the alpha-hemolysin nanopore, we show that in the presence of Ag+, duplex stability is most increased for the cytosine-cytosine (C-C) pair, followed by the cytosine-methylcytosine (C-mC) pair and the cytosine-hydroxymethylcytosine (C-hmC) pair, which has no observable Ag+ induced stabilization. Molecular dynamics simulations reveal that the hydrogen-bond-mediated paring of a C-C mismatch results in a binding site for Ag+. Cytosine modifications (such as mC and hmC) disrupted the hydrogen bond, resulting in disruption of the Ag+ binding site. Our experimental method provides a novel platform to study the metal ion-DNA interactions and could also serve as a direct detection method for nucleobase modifications.

Quantifying the Sensitivity of Scent Detection Dogs To Identify Fecal Contamination on Raw Produce

Consumption of raw produce commodities has been associated with foodborne outbreaks in the United States. In a recent Centers for Disease Control and Prevention report outlining the incidence of food-related outbreaks from 1998 to 2008, produce of all kinds were implicated in 46% of illnesses and 23% of deaths. Methods that quickly identify fecal contamination of foods, including produce, will allow prioritization of samples for testing during investigations and perhaps decrease the time required to identify specific brands or lots. We conducted a series of trials to characterize the sensitivity and specificity of scent detection dogs to accurately identify fecal contamination on raw agricultural commodities (romaine lettuce, spinach, cilantro, and roma tomatoes). Both indirect and direct methods of detection were evaluated. For the indirect detection method, two dogs were trained to detect contamination on gauze pads previously exposed to produce contaminated with feces. For the direct detection method, two dogs were trained to identify fecal contamination on fresh produce. The indirect method did not result in acceptable levels of sensitivity except for the highest levels of fecal contamination (25 g of feces). Each dog had more difficulty detecting fecal contamination on cilantro and spinach than on roma tomatoes. For the direct detection method, the dogs exhibited >75% sensitivity for detecting ≥0.25 g of feces on leafy greens (cilantro, romaine lettuce, and spinach) and roma tomatoes, with sensitivity declining as the amount of feces dropped below 0.025 g. We determined that use of a scent detection dog to screen samples for testing can increase the probability of detecting ≥0.025 g of fecal contamination by 500 to 3,000% when samples with fecal contamination are rare (≤1%).