Collection Path Research Articles

High-Responsivity Si Photodiodes at 1060 nm in Standard CMOS Technology

Photodetection with high responsivity at the wavelength of 1060 nm is highly desirable for light detection and ranging (LiDAR) as well as the recent emergence of swept-source optical coherent tomography (SS-OCT) applications. However, the absorption coefficient $\alpha $ of Si material at 1060 nm under the bias of 0 V is very low due to its approach to the absorption bandgap edge of Si material. In this letter, the carrier-collection-enhanced structure is proposed, which functions as multiple carrier collection paths, which enhances the external quantum efficiency of photodiodes. An efficient Si photodiode with responsivity of 0.49 A/W at 1060 nm at 0 V is demonstrated, which is 2.5 times of that of commercial products. The cost-effective fabrication of Si photodiodes greatly enhances the system performance of LiDAR and OCT.

Location‐dependent sensing data collection and processing mechanism in vehicular network

AbstractWith the promotion of the Internet of Things, in which a growing number of objects in everyday life are able to communicate with each other, crowdsensing has attracted public attention. Among different devices, vehicles with various sensors can perform the traffic data collection tasks released by the traffic center, which is helpful for monitoring road conditions. Thus, we use crowdsensing between vehicles to improve the precision of traffic state estimation. We also propose a location‐dependent sensing task assignment mechanism for traffic data collection and a multisource data fusion model for traffic data processing in a vehicular network. First, we establish a mathematical model for the sensing task assignment considering the vehicle's time budget constraint, location, and collection task requirements. We then propose a task assignment algorithm consisting of determining the order for vehicle allocation and scheduling the optimal collection path for each vehicle, which aims to achieve maximum platform utility. Furthermore, we put forward a fusion model, including spatial fusion and temporal fusion, to better process the collected data. We use a power average operator for the spatial fusion and a temporal correlation–based data compression algorithm for the temporal fusion. The obtained simulation results validate the accuracy and correctness of our approach.

EAPC: Energy-Aware Path Construction for Data Collection Using Mobile Sink in Wireless Sensor Networks

Data collection is one of the paramount concerns in wireless sensor networks. Many data collection algorithms have been proposed for collecting data in particular monitoring regions. However, the efficiency of the paths for such data collection can be improved. This paper proposes an energy-aware path construction (EAPC) algorithm, which selects an appropriate set of data collection points, constructs a data collection path, and collects data from the points burdened with data. EAPC is intended to prolong the network lifetime, it accounts for the path cost from its current data collection point to the next point and the forwarding load of each sensor node. Performance evaluation reveals that the proposed EAPC has more efficient performance than existing data collection mechanisms in terms of network lifetime, energy consumption, fairness index, and efficiency index.

Adaptive Transmission Range Based Topology Control Scheme for Fast and Reliable Data Collection

An Adaptive Transmission Range Based Topology Control (ATRTC) scheme is proposed to reduce delay and improve reliability for data collection in delay and loss sensitive wireless sensor network. The core idea of the ATRTC scheme is to extend the transmission range to speed up data collection and improve the reliability of data collection. The main innovations of our work are as follows: (1) an adaptive transmission range adjustment method is proposed to improve data collection reliability and reduce data collection delay. The expansion of the transmission range will allow the data packet to be received by more receivers, thus improving the reliability of data transmission. On the other hand, by extending the transmission range, data packets can be transmitted to the sink with fewer hops. Thereby the delay of data collection is reduced and the reliability of data transmission is improved. Extending the transmission range will consume more energy. Fortunately, we found the imbalanced energy consumption of the network. There is a large amount of energy remains when the network died. ATRTC scheme proposed in this paper can make full use of the residual energy to extend the transmission range of nodes. Because of the expansion of transmission range, nodes in the network form multiple paths for data collection to the sink node. Therefore, the volume of data received and sent by the near‐sink nodes is reduced, the energy consumption of the near‐sink nodes is reduced, and the network lifetime is increased as well. (2) According to the analysis in this paper, compared with the CTPR scheme, the ATRTC scheme reduces the maximum energy consumption by 9%, increases the network lifetime by 10%, increases the data collection reliability by 7.3%, and reduces the network data collection time by 23%.

An efficient data delivery mechanism for AUV-based Ad hoc UASNs

Existing 3D Underwater Acoustic Sensor Networks (UASNs) are either fixed having nodes anchored with the seabed or a combination of Autonomous Underwater Vehicles (AUVs) and a fixed UASN where AUVs are controlled to move along paths for data collection. Existing data delivery protocols for such AUV equipped networks are designed in a way where AUVs act as message ferries. These UASNs are deployed for a specific service such as asset (e.g., oil pipes, shipwreck) monitoring and event detection. For a coordinated data collection, to deploy a network for any service like information discovery in an ad hoc manner, it requires a 3D UASN consisting of only AUVs and the movement of an AUV needs to be controlled by another AUV through commands. To our knowledge, no such data delivery protocol required for a 3D UASN comprising only AUVs exists in the current literature that can efficiently handle data collection and delivery. To address this research gap, in this paper, an AUV-based technique for ad hoc underwater network, namely AUV-based Data Delivery Protocol (ADDP), is introduced which ensures data delivery within a given time-constraint by controlling node (i.e., AUV) movement at each hop through commands of a node. The performance of the proposed protocol has also been evaluated and compared with existing relevant protocols in terms of packet delivery ratio, routing overhead and energy consumption considering various network scenarios and sizes. Results exhibit outstanding performance improvement achieved by the proposed protocol for all metrics.

Silicon nitride waveguide platform for fluorescence microscopy of living cells.

Waveguide chip-based microscopy reduces the complexity of total internal reflection fluorescence (TIRF) microscopy, and adds features like large field of view illumination, decoupling of illumination and collection path and easy multimodal imaging. However, for the technique to become widespread there is a need of low-loss and affordable waveguides made of high-refractive index material. Here, we develop and report a low-loss silicon nitride (Si3N4) waveguide platform for multi-color TIRF microscopy. Single mode conditions at visible wavelengths (488-660 nm) were achieved using shallow rib geometry. To generate uniform excitation over appropriate dimensions waveguide bends were used to filter-out higher modes followed by adiabatic tapering. Si3N4 material is finally shown to be biocompatible for growing and imaging living cells.

Desire lines and defensive architecture in modern urban environments

Public space is being increasingly managed by defensive architecture, surveillance and other subtle filtering mechanisms to make it more palatable and attendant to the needs of capital. This reinforces social boundaries, making space inhospitable to those people whose presence is not welcome, and serves to ‘discipline’ city inhabitants into primarily consumption based modes of interacting with and in the city. However, disenfranchised urban populations still find ways to exist in and navigate these spaces. The purpose of this article is to highlight these ways by introducing the concept of ‘desire lines’ as a means of overcoming or re-imagining defensive space. We use Deleuze and Guattari’s theory of desire as productive force, combined with De Certeau’s notion of ‘walking the city’, to explore how individuals and social movements might practically, and in a metaphorical sense, create new collective paths, creating ‘desire lines’ of resistance and change within what is often an increasingly unforgiving and dominated urban environment, created by and for capital at the expense of a vibrant public realm.

Resonance Fluorescence of an InGaAs Quantum Dot in a Planar Cavity Using Orthogonal Excitation and Detection.

The ability to perform simultaneous resonant excitation and fluorescence detection is important for quantum optical measurements of quantum dots (QDs). Resonant excitation without fluorescence detection - for example, a differential transmission measurement - can determine some properties of the emitting system, but does not allow applications or measurements based on the emitted photons. For example, the measurement of photon correlations, observation of the Mollow triplet, and realization of single photon sources all require collection of the fluorescence. Incoherent excitation with fluorescence detection - for example, above band-gap excitation - can be used to create single photon sources, but the disturbance of the environment due to the excitation reduces the indistinguishability of the photons. Single photon sources based on QDs will have to be resonantly excited to have high photon indistinguishability, and simultaneous collection of the photons will be necessary to make use of them. We demonstrate a method to resonantly excite a single QD embedded in a planar cavity by coupling the excitation beam into this cavity from the cleaved face of the sample while collecting the fluorescence along the sample's surface normal direction. By carefully matching the excitation beam to the waveguide mode of the cavity, the excitation light can couple into the cavity and interact with the QD. The scattered photons can couple to the Fabry-Perot mode of the cavity and escape in the surface normal direction. This method allows complete freedom in the detection polarization, but the excitation polarization is restricted by the propagation direction of the excitation beam. The fluorescence from the wetting layer provides a guide to align the collection path with respect to the excitation beam. The orthogonality of the excitation and detection modes enables resonant excitation of a single QD with negligible laser scattering background.

Efficient Data Collection by Mobile Sink to Detect Phenomena in Internet of Things

With the rapid development of Internet of Things (IoT), more and more static and mobile sensors are being deployed for sensing and tracking environmental phenomena, such as fire, oil spills and air pollution. As these sensors are usually battery-powered, energy-efficient algorithms are required to extend the sensors’ lifetime. Moreover, forwarding sensed data towards a static sink causes quick battery depletion of the sinks’ nearby sensors. Therefore, in this paper, we propose a distributed energy-efficient algorithm, called the Hilbert-order Collection Strategy (HCS), which uses a mobile sink (e.g., drone) to collect data from a mobile wireless sensor network (mWSN) and detect environmental phenomena. The mWSN consists of mobile sensors that sense environmental data. These mobile sensors self-organize themselves into groups. The sensors of each group elect a group head (GH), which collects data from the mobile sensors in its group. Periodically, a mobile sink passes by the locations of the GHs (data collection path) to collect their data. The collected data are aggregated to discover a global phenomenon. To shorten the data collection path, which results in reducing the energy cost, the mobile sink establishes the path based on the order of Hilbert values of the GHs’ locations. Furthermore, the paper proposes two optimization techniques for data collection to further reduce the energy cost of mWSN and reduce the data loss.

Functionalization of Silicon Nanostructures for Energy-Related Applications.

Silicon (Si) is used in various application fields such as solar cells and electric devices. Functionalization of Si nanostructures is one way to further improve the properties of these devices such as these. This Review summarizes recent results of solar cell and Li-ion battery applications using Si-related nanostructures. In solar cell applications, the light trapping effect is increased and the carrier recombination rate is decreased due to the short carrier collection path achieved by radially constructed p-n junction in Si nanowires, resulting in higher power conversion efficiency. The nonradiative energy transfer effect created by nanocrystalline Si is a novel way of improving solar cell properties. Si-related nanostructures are also anticipated as new anode materials with higher capacity in Li-ion batteries. Si-related nanocomposite materials which show densely packed microparticle structures agglomerated with small nanoparticles are described here as a promising challenge. These unique structures show higher capacity and longer cycle properties.

Preparing Students for a Diverse, Deliberative Democracy: College Diversity Experiences and Informed Citizenship after College

Background/Context The role of race in the university continues to be a contentious issue. Proponents of college diversity often cite the importance of fostering a diverse and deliberative democratic society, but the link between student experiences and postcollege citizenship has received limited attention. Purpose/Objective This study explores the extent to which two types of college diversity experiences (cross-racial interaction and curricular/co-curricular diversity engagement) predict aspects of informed citizenship associated with supporting a deliberative democracy six years after graduation (i.e., following the news, discussion of racial issues, and importance of keeping up to date with politics). Participants The dataset for this study came from UCLA's Higher Education Research Institute. We utilized the 1994–1998–2004 cohort of students/alumni, which included a postcollege survey administered six years after graduation. The total sample consisted of 8,634 alumni from 229 institutions. Research Design This study utilized secondary data analysis of the 1994–1998–2004 CIRP dataset. Data Collection and Analysis Path analysis was particularly useful for this study to examine the direct and indirect effects of the college diversity experiences on senior-year and longer-term outcomes. Results College diversity experiences have direct effects on postcollege discussions of racial issues, which suggests that these forms of engagement may have long-lasting effects on college graduates. Moreover, curricular/co-curricular diversity engagement also has positive, indirect effects on keeping up to date with politics, news consumption, and discussing racial issues well after graduation. The pattern of findings differed when analyzed separately by racial/ethnic group (i.e., Whites/Caucasians, Asian Americans, and underrepresented students of color). Conclusions/Recommendations This study adds to the existing knowledge base by making a key contribution to the limited research on the long-term benefits of diversity experiences as well as the dimensions of higher education that inform active citizenship in a deliberative democracy. This study examined the complex relationships—both direct and indirect effects—associated with these college diversity experiences and outcomes after college and how these relationships vary by racial/ethnic group. The current findings point to the particular importance of maximizing opportunities for cross-racial interaction and curricular/co-curricular diversity engagement for all students regardless of their race/ethnicity.

Adiabatic self-consistent collective path in nuclear fusion reactions

Collective reaction paths for fusion reactions, $^{16}$O+$\alpha$ $\rightarrow$ $^{20}$Ne and $^{16}$O+$^{16}$O $\rightarrow$ $^{32}$S, are microscopically determined, on the basis of the adiabatic self-consistent collective coordinate (ASCC) method. The collective path is maximally decoupled from other intrinsic degrees of freedom. The reaction paths turn out to deviate from those obtained with standard mean-field calculations with constraints on quadrupole and octupole moments. The potentials and inertial masses defined in the ASCC method are calculated along the reaction paths. The sub-barrier fusion cross sections are calculated for these systems. Inertial mass inside the Coulomb barrier may have a significant influence on the fusion cross section at the deep sub-barrier energy.

Tracing the Potential Flow of Consumer Data: A Network Analysis of Prominent Health and Fitness Apps

BackgroundA great deal of consumer data, collected actively through consumer reporting or passively through sensors, is shared among apps. Developers increasingly allow their programs to communicate with other apps, sensors, and Web-based services, which are promoted as features to potential users. However, health apps also routinely pose risks related to information leaks, information manipulation, and loss of information. There has been less investigation into the kinds of user data that developers are likely to collect, and who might have access to it.ObjectiveWe sought to describe how consumer data generated from mobile health apps might be distributed and reused. We also aimed to outline risks to individual privacy and security presented by this potential for aggregating and combining user data across apps.MethodsWe purposively sampled prominent health and fitness apps available in the United States, Canada, and Australia Google Play and iTunes app stores in November 2015. Two independent coders extracted data from app promotional materials on app and developer characteristics, and the developer-reported collection and sharing of user data. We conducted a descriptive analysis of app, developer, and user data collection characteristics. Using structural equivalence analysis, we conducted a network analysis of sampled apps’ self-reported sharing of user-generated data.ResultsWe included 297 unique apps published by 231 individual developers, which requested 58 different permissions (mean 7.95, SD 6.57). We grouped apps into 222 app families on the basis of shared ownership. Analysis of self-reported data sharing revealed a network of 359 app family nodes, with one connected central component of 210 app families (58.5%). Most (143/222, 64.4%) of the sampled app families did not report sharing any data and were therefore isolated from each other and from the core network. Fifteen app families assumed more central network positions as gatekeepers on the shortest paths that data would have to travel between other app families.ConclusionsThis cross-sectional analysis highlights the possibilities for user data collection and potential paths that data is able to travel among a sample of prominent health and fitness apps. While individual apps may not collect personally identifiable information, app families and the partners with which they share data may be able to aggregate consumer data, thus achieving a much more comprehensive picture of the individual consumer. The organizations behind the centrally connected app families represent diverse industries, including apparel manufacturers and social media platforms that are not traditionally involved in health or fitness. This analysis highlights the potential for anticipated and voluntary but also possibly unanticipated and involuntary sharing of user data, validating privacy and security concerns in mobile health.

Embedded Metal Electrode for Organic-Inorganic Hybrid Nanowire Solar Cells.

We demonstrate here an embedded metal electrode for highly efficient organic-inorganic hybrid nanowire solar cells. The electrode proposed here is an effective alternative to the conventional bus and finger electrode which leads to a localized short circuit at a direct Si/metal contact and has a poor collection efficiency due to a nonoptimized electrode design. In our design, a Ag/SiO2 electrode is embedded into a Si substrate while being positioned between Si nanowire arrays underneath poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), facilitating suppressed recombination at the Si/Ag interface and notable improvements in the fabrication reproducibility. With an optimized microgrid electrode, our 1 cm2 hybrid solar cells exhibit a power conversion efficiency of up to 16.1% with an open-circuit voltage of 607 mV and a short circuit current density of 34.0 mA/cm2. This power conversion efficiency is more than twice as high as that of solar cells using a conventional electrode (8.0%). The microgrid electrode significantly minimizes the optical and electrical losses. This reproducibly yields a superior quantum efficiency of 99% at the main solar spectrum wavelength of 600 nm. In particular, our solar cells exhibit a significant increase in the fill factor of 78.3% compared to that of a conventional electrode (61.4%); this is because of the drastic reduction in the metal/contact resistance of the 1 μm-thick Ag electrode. Hence, the use of our embedded microgrid electrode in the construction of an ideal carrier collection path presents an opportunity in the development of highly efficient organic-inorganic hybrid solar cells.

Supercritical angle Raman microscopy: a surface-sensitive nanoscale technique without field enhancement

Raman scattering microscopy is a versatile tool for label-free imaging and molecular fingerprint analysis. Here, we provide the first demonstration that the selective collection of scattered signals exceeding the critical angle for total internal reflection enables surface-confined spontaneous Raman investigations at nanometre resolution. This high-axial selectivity leads to improved signal-to-background ratios, thus making this technique an excellent probe for surface-related molecular specimens. The richness of the spectroscopic information obtained through the supercritical angle Raman (SAR) collection path was proven by comparing its output with that of a parallel far-field collection path. Furthermore, we demonstrated that the proposed SAR technique is a versatile microscopy approach that can be used alone or in combination with amplified Raman modalities such as surface-enhanced resonance Raman scattering.

Urchin-inspired ZnO-TiO2 core-shell as building blocks for dye sensitized solar cells

We applied the core-shell concept to an urchin-inspired ZnO nanowire photoanode building block as a means to increase the electron transport and reduce recombination between nanowire and electrolyte. Dye-sensitized solar cells (DSSCs) were prepared, for the first time, from arrays of urchin-like ZnO nanowire building blocks covered with a thin layer of anatase TiO2 by atomic layer deposition (ALD). An increase in the cell open-circuit voltage (VOC) and an improvement in the conversion efficiency were observed when the urchin-like ZnO building blocks were coated with 10nm thick TiO2 ALD shells in combination with 10μm thick top layer of TiO2 nanoparticles of 15.8nm size. Using urchin-like ZnO nanowires as building blocks can improve the light-scattering and provide a higher surface area with a great control of the nanowire dimensions to increase the dye loading and reduce the electron collection path. The addition of a thin TiO2 blocking layer decreases the recombination of charges in such a high surface area nanostructure.

Fe2O3 Nanoneedles on Ultrafine Nickel Nanotube Arrays as Efficient Anode for High‐Performance Asymmetric Supercapacitors

High performance of electrochemical energy storage devices depends on the smart structure engineering of electrodes, including the tailored nanoarchitectures of current collectors and subtle hybridization of active materials. To improve the anode supercapacitive performance of Fe2O3 for high‐voltage asymmetric supercapacitors, here, a hybrid core‐branch nanoarchitecture is proposed by integrating Fe2O3 nanoneedles on ultrafine Ni nanotube arrays (NiNTAs@Fe2O3 nanoneedles). The fabrication process employs a bottom‐up strategy via a modified template‐assisted method starting from ultrafine ZnO nanorod arrays, ensuring the formation of ultrafine Ni nanotube arrays with ultrathin tube walls. The novel developed NiNTAs@Fe2O3 nanoneedle electrode is demonstrated to be a highly capacitive anode (418.7 F g−1 at 10 mV s−1), matching well with the similarly built NiNTAs@MnO2 nanosheet cathode. Contributed by the efficient electron collection paths and short ion diffusion paths in the uniquely designed anode and cathode, the asymmetric supercapacitors exhibit an excellent maximum energy density of 34.1 Wh kg−1 at the power density of 3197.7 W kg−1 in aqueous electrolyte and 32.2 Wh kg−1 at the power density of 3199.5 W kg−1 in quasi‐solid‐state gel electrolyte.

Energy-efficient mobile data collection adopting node cooperation in an underwater acoustic sensor network

This paper considers an underwater acoustic sensor network with one mobile surface node to collect data from multiple underwater nodes, where the mobile destination requests retransmission from each underwater node individually employing traditional automatic-repeat-request (ARQ) protocol. We propose a practical node cooperation (NC) protocol to enhance the collection efficiency, utilizing the fact that underwater nodes can overhear the transmission of others. To reduce the source level of underwater nodes, the underwater data collection area is divided into several sub-zones, and in each sub-zone, the mobile surface node adopting the NC protocol could switch adaptively between selective relay cooperation (SRC) and dynamic network coded cooperation (DNC). The difference of SRC and DNC lies in whether or not the selected relay node combines the local data and the data overheard from undecoded node(s) to form network coded packets in the retransmission phase. The NC protocol could also be applied across the sub-zones due to the wiretap property. In addition, we investigate the effects of different mobile collection paths, collection area division and cooperative zone design for energy saving. The numerical results show that the proposed NC protocol can effectively save energy compared with the traditional ARQ scheme.

Self-consistent collective coordinate for reaction path and inertial mass

We propose a numerical method to determine the optimal collective reaction path for the nucleus-nucleus collision, based on the adiabatic self-consistent collective coordinate (ASCC) method. We use an iterative method combining the imaginary-time evolution and the finite amplitude method, for the solution of the ASCC coupled equations. It is applied to the simplest case, the $\alpha-\alpha$ scattering. We determine the collective path, the potential, and the inertial mass. The results are compared with other methods, such as the constrained Hartree-Fock method, the Inglis's cranking formula, and the adiabatic time-dependent Hartree-Fock (ATDHF) method.

Enhancement of short-circuit current density in Cu2O/ZnO heterojunction solar cells

This study reports the achievement of a high short-circuit current density (Jsc) of 9.53 mA/cm2 for low-cost electrodeposited (ED) semi-transparent Cu2O/ZnO nanorod (NR) solar cells. High-quality chemical-bath-deposited ZnO NRs that align with the carrier collection path were used to replace the traditional sputtered ZnO film. An almost four-fold increase (from 1.63 to 6.41 mA/cm2) in Jsc was obtained with the NRs compared to the level obtained with a sputtered ZnO thin film cell. Decreased the ED Cu2O absorber film thickness is able to compensate for the recombination loss that results from Cu2O's short minority carrier drift and diffusion length (both on the order of 100 nm), further boosting Jsc to 7.77 mA/cm2. Additional photo-generated carriers were created for the semi-transparent solar cells when a silver mirror was deposited on the backside of the glass; this further enhanced absorption and improved Jsc to 9.53 mA/cm2. This is the highest Jsc value reported to date for a low-cost ED Cu2O/ZnO solar cell.