Giovanni Tapang

Self-organized queuing and scale-free behavior in real escape panic

Numerical investigations of escape panic of confined pedestrians have revealed interesting dynamical features such as pedestrian arch formation around an exit, disruptive interference, self-organized queuing, and scale-free behavior. However, these predictions have remained unverified because escape panic experiments with real systems are difficult to perform. For mice escaping out of a water pool, we found that for a critical sampling rate the escape behavior exhibits the predicted features even at short observation times. The mice escaped via an exit in bursts of different sizes that obey exponential and (truncated) power-law distributions depending on exit width. Oversampling or undersampling the mouse escape rate prevents the observation of the predicted features. Real systems are normally subject to unavoidable constraints arising from occupancy rate, pedestrian exhaustion, and nonrigidity of pedestrian bodies. The effect of these constraints on the dynamics of real escape panic is also studied.

Streaming, disruptive interference and power-law behavior in the exit dynamics of confined pedestrians

We analyze the exit dynamics of pedestrians who are initially confined in a room. Pedestrians are modeled as cellular automata and compete to escape via a known exit at the soonest possible time. A pedestrian could move forward, backward, left or right within each iteration time depending on adjacent cell vacancy and in accordance with simple rules that determine the compulsion to move and physical capability relative to his neighbors. The arching signatures of jamming were observed and the pedestrians exited in bursts of various sizes. Power-law behavior is found in the burst-size frequency distribution for exit widths w greater than one cell dimension (w>1). The slope of the power-law curve varies with w from −1.3092(w=2) to −1.0720(w=20). Streaming which is a diffusive behavior, arises in large burst sizes and is more likely in a single-exit room with w=1 and leads to a counterintuitive result wherein an average exit throughput Q is obtained that is higher than with w=2,3, or 4. For a two-exit room (w=1), Q is not greater than twice the yield of a single-exit room. If the doors are not separated far enough (<4w), Q becomes even significantly less due to a collective slow-down that emerges among pedestrians crossing in each others path (disruptive interference effect). For the same w and door number, Q is also higher with relaxed pedestrians than with anxious ones.

Dynamic-range enhancement of an optimized 1-bit A/D converter

A technique is demonstrated for extending the dynamic range of 1-bit analog-to-digital converters (ADCs) that sample at the maximum rate using a sinusoid reference r(t)=A/sub r/ cos(2/spl pi/f/sub r/t). The ADC has a detection limit B=/spl pi/A/sub r//spl delta///spl utri/, where 2/spl delta//sub s/ is the base-clock period, and /spl utri/=sampling interval=1/2f/sub r//spl ges/2/spl delta/. Optimal sampling is achieved at /spl utri/=2/spl delta/, but with large quantization errors found in the sampled representation of the input signal s(t). Dithering with noise n/sub /spl sigma//(t) of appropriate variance /spl sigma//sup 2/ is utilized to measure a subthreshold s(t) where |s(t)|<B for all t. Both uniform white noise (UWN) and Gaussian white noise (GWN) are utilized. With UWN dithering at /spl sigma/=B, we could reduce the errors to levels that are produced by an equivalent q-bit amplitude-sampling (bipolar) ADC by observing the dithered signal s(t)+n/sub /spl sigma//(t) over a time duration of T[(0.116/|V|)(2/sup q/-1)]/sup 0.995/, where T is the sampling period, and /spl plusmn/V are the ADC supply voltages. With GWN dithering at /spl sigma/=0.5 B, the duration required is T[(0.109/V)(2/sup q/-1)]/sup 0.996/.

PROSE AND POETRY CLASSIFICATION AND BOUNDARY DETECTION USING WORD ADJACENCY NETWORK ANALYSIS

Word adjacency networks constructed from written works reflect differences in the structure of prose and poetry. We present a method to disambiguate prose and poetry by analyzing network parameters of word adjacency networks, such as the clustering coefficient, average path length and average degree. We determine the relevant parameters for disambiguation using linear discriminant analysis (LDA) and the effect size criterion. The accuracy of the method is 74.9 ± 2.9% for the training set and 73.7 ± 6.4% for the test set which are greater than the acceptable classifier requirement of 67.3%. This approach is also useful in locating text boundaries within a single article which falls within a window size where the significant change in clustering coefficient is observed. Results indicate that an optimal window size of 75 words can detect the text boundaries.

Independent light fields generated using a phase-only spatial light modulator

We present a method of reshaping light in three dimensions via phase modulation. The method calculates the target computer-generated hologram individually and adds to it an appropriate transfer function to translate the reconstruction to any location in space. We are able to simultaneously generate independently controlled arbitrary patterns at different positions using a single laser beam.

Preserved Network Metrics Across Translated Texts

Co-occurrence language networks based on Bible translations and the Universal Declaration of Human Rights (UDHR) translations in different languages were constructed and compared with random text networks. Among the considered network metrics, the network size, N, the normalized betweenness centrality (BC), and the average k-nearest neighbors, knn, were found to be the most preserved across translations. Moreover, similar frequency distributions of co-occurring network motifs were observed for translated texts networks.

CHARACTERIZING ENGLISH POETIC STYLE USING COMPLEX NETWORKS

Complex networks have been proven useful in characterizing written texts. Here, we use networks to probe if there exist a similarity within, and difference across, era as reflected within the poems structure. In literary history, boundary lines are set to distinguish the change in writing styles through time. We obtain the network parameters and motif frequencies of 845 poems published from 1522 to 1931 and relate this to the writing of the Elizabethan, 17th Century, Augustan, Romantic and Victorian eras. Analysis of the different network parameters shows a significant difference of the Augustan era (1667–1780) with the rest. The network parameters and the convex hull and centroids of the motif frequencies reflect the adjectival sequence pattern of the poems of the Augustan era.

Behavior of the point-spread function in photon-limited confocal microscopy.

We study the behavior of the point-spread function (PSF) of the confocal scanning optical microscope (CSOM) when the available optical energy density from the sample plane is low (<7.5 microJoule/micrometers2). The PSF profile is analyzed under three photon-limited imaging conditions: (1) reflection-type CSOM with a weak source and a perfectly reflecting sample, (2) reflection-type CSOM with a strong illumination source and a weak sample, and (3) fluorescence CSOM with a weak fluorescent sample. Linfoots image quality criteria of fidelity, structural content, and correlation quality are used to assess the reproducibility of the PSF profile as a function of the photon number. Low photon numbers yield a PSF profile that is difficult to maintain from one location in the sample plane to another. The optical sectioning capability of the CSOM was found to deteriorate more quickly against light power reduction than its transverse resolving power. The signal-to-noise ratio of the scanned CSOM image improves exponentially with the photon number from the sample plane. The noise that is generated by an unstable PSF has an average amplitude that decreases exponentially with the photon number and is significant only at low photon numbers. The CSOM image quality deteriorates because of spurious high-frequency components, degradation in the PSF dynamic range, and varying resolving power.

TEXTING STYLES AND INFORMATION CHANGE OF SMS TEXT MESSAGES IN FILIPINO

We identify the different styles of texting in Filipino short message service (SMS) texts and analyze the change in unigram and bigram frequencies due to these styles. Style preference vectors for sample texts were calculated and used to identify the style combination used by an average individual. The change in Shannon entropy of the SMS text is explained in light of a coding process.

Characterization of the Performance of a 7-Mirror Segmented Reflecting Telescope via the Angular Spectrum Method

A segmented reflecting telescope made of seven 76 mm concave mirrors, each with a focal length of 300 mm, was characterized. Its performance was evaluated by computing the point spread function (PSF) and comparing it to an equivalent monolithic mirror. Aberrations were added and corrected using a phase retrieval technique called the Gerchberg-Saxton (GS) algorithm to obtain the correction phase that serves as the input to the spatial light modulator (SLM). Results revealed an improvement in the telescope angular resolution as a result of the implemented phase correction. It was also shown that the PSF varies depending on the orientation and number of mirrors added.