Caesar Saloma

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.

Monte Carlo analysis of two-photon fluorescence imaging through a scattering medium

The behavior of two-photon fluorescence imaging through a scattering medium is analyzed by use of the Monte Carlo technique. The axial and transverse distributions of the excitation photons in the focused Gaussian beam are derived for both isotropic and anisotropic scatterers at different numerical apertures and at various ratios of the scattering depth with the mean free path. The two-photon fluorescence profiles of the sample are determined from the square of the normalized excitation intensity distributions. For the same lens aperture and scattering medium, two-photon fluorescence imaging offers a sharper and less aberrated axial response than that of single-photon confocal fluorescence imaging. The contrast in the corresponding transverse fluorescence profile is also significantly higher. Also presented are results comparing the effects of isotropic and anisotropic scattering media in confocal reflection imaging. The convergence properties of the Monte Carlo simulation are also discussed.

Classification of coral reef images from underwater video using neural networks

We use a feedforward backpropagation neural network to classify close-up images of coral reef components into three benthic categories: living coral, dead coral and sand. We have achieved a success rate of 86.5% (false positive = 6.7%) for test images that were not in the training set which is high considering that corals occur in an immense variety of appearance. Color and texture features derived from video stills of coral reef transects from the Great Barrier Reef were used as inputs to the network. We also developed a rule-based decision tree classifier according to how marine scientists classify corals from texture and color, and obtained a lower recognition rate of 79.7% for the same set of images.

Colored object recognition by digital holography and a hydrogen Raman shifter

Multi-wavelength holography is demonstrated with a H(2) Raman shifter that is pumped with an elliptically-polarized pulsed 532 nm beam to produce temporally coherent, intense, polarized output lines. Digital holograms of two-dimensional colored objects are recorded using Raman output lines at 630.4 nm (S(05), Red), 532 nm (Rayleigh, Green) and 435.7 nm (aS(10), Blue). Object reconstruction is done numerically via the convolution method and colored object recognition is achieved by multi-channel correlation of the Red, Green, and Blue reconstructions of the reference and the target object.

Curve spreads: a biometric from front-view gait video

We introduce the curve spread as an efficient descriptor of front-view gait of humans walking towards a camera. The curve spread is a compact two-dimensional representation of the time-variations of a moving body outline. Most gait biometrics employ features derived from side-view videos because limb swings are more pronounced from the side than from the front. However, side-view observations are often impractical and incompatible with the ability of humans to recognize others from front-view gait. Identification tests using cross correlation of curve spreads of 12 videos from 4 walking subjects, yielded 100% recognition rate.

Reconstructing the Hartley intensity spectrum from its sinusoidal crossings

It is shown that a 2M-point representation I(H)(f) of the Hartley intensity spectrum I(Ha)(f) can be reconstructed from the intersections of I(Ha)(f) with the reference sinusoid R(f) of period 2delta. As required by the Nyquist sampling criterion, one sinusoidal crossing is detected within every frequency interval delta when the bandwidth of I(H)(f) is 2Mdelta. Specifically, the 2M crossings are used to determine the 2M expansion coefficients [h(mDelta)] of I(H)(f) with respect to the Hartley basis functions: cass(2pifmDelta), where Delta = /Mdelta and m = -M, -M + 1, ...,M. An accurate and efficient algorithm for computing [h(mDelta)] from the sinusoidal crossings also is proposed and demonstrated.

Advantages of two-color excitation fluorescence microscopy with two confocal excitation beams

Abstract We establish the advantages of two-color excitation (2CE) fluorescence microscopy where the two confocal excitation beams are separated by an angle, θ [Opt. Lett. 24 (1999) 1505]. The two excitation wavelengths λ 1 and λ 2 are related according to 1/ λ e =1/ λ 1 +1/ λ 2 , where λ e is the single-photon excitation wavelength of the sample. Both circular and annular pupils are considered in the calculation of the three-dimensional point spread function of the 2CE microscope. When λ 1 ≠ λ 2 , the 2CE fluorescence intensity is proportional to the product of the two excitation intensities and is generated only in regions where the excitation beams overlap with each other in both space and time. Two-photon excitation fluorescence (2PE) microscopy is a special case of 2CE microscopy with λ 1 = λ 2 =2 λ e = λ 2p . With focusing lenses of low-to-moderate numerical apertures, the main advantage of 2CE microscopy over its 2PE counterpart is not in improved imaging resolution, but in the observation of microscopic objects through highly scattering media. In 2CE imaging, scattering decreases the in-focus fluorescence but only minimally increases the unwanted fluorescence background unlike in the 2PE case. Furthermore, annular lenses with their very long depths of field offer an easier way for maintaining the alignment of the two confocal excitation beams in applications involving the imaging of irregularly shaped, thick samples.

Site-specific confocal fluorescence imaging of biological microstructures in a turbid medium

Normally transparent biological structures in a turbid medium are imaged using a laser confocal microscope and multiwavelength site-specific fluorescence labelling. The spatial filtering capability of the detector pinhole in the confocal microscope limits the number of scattered fluorescent photons that reach the photodetector. Simultaneous application of different fluorescent markers on the same sample site minimizes photobleaching by reducing the excitation time for each marker. A high-contrast grey-level image is also produced by summing confocal images of the same site taken at different fluorescence wavelengths. Monte Carlo simulations are performed to obtain the quantitative behaviour of confocal fluorescence imaging in turbid media. Confocal images of the following samples were also obtained: (i) 15 microm diameter fluorescent spheres placed 1.16 mm deep beneath an aqueous suspension of 0.0823 microm diameter polystyrene latex spheres, and (ii) hindbrain of a whole-mount mouse embryo (age 10 days) that was stained to fluoresce at 515 nm and 580 nm peak wavelengths. Expression of RNA transcripts of a gene within the embryo hindbrain was detected by a fluorescence-based whole-mount in situ hybridization procedure that we recently tested.

Herding in Real Escape Panic

We introduce the element of copying in an agent-based model of escape panic to describe with greater accuracy the exit behavior of mice that are escaping from a flooded two-exit chamber. Aside from the panic threshold ϕ (0 ≤ ϕ ≤ 5), our model utilizes the imitation tendency α (0 ≤ α ≤ 1) such that agents with ϕ = 0, are calm and tend to stay put while those that are likely to copy their neighbors are described by large α values. A high degree of copying among escaping agents favors the emergence of herding behavior. Both the Moore and the von Neumann neighborhood are tried to depict the movement of agents in a plane. Herding decreases the exit throughput Q by causing an inefficient utilization of the two available exits for escape. The dependence of Q with α and the exit door separation are highly nonlinear. The inclusion of α has significantly improved the capability of our model to explain the Q-behavior that was observed in the mice experiments. Interestingly, simulation results show that copying could promote faster room evacuation at α ≈ 0.5 and especially at high room occupancy rates (> 60%). At α ≈ 0.5, an agent is equally likely to copy or ignore the action of its neighbor.