Two-way Transfer Research Articles

Femtosecond time synchronization of optical clocks off of a flying quadcopter

Future optical clock networks will require free-space optical time-frequency transfer between flying clocks. However, simple one-way or standard two-way time transfer between flying clocks will completely break down because of the time-of-flight variations and Doppler shifts associated with the strongly time-varying link distances. Here, we demonstrate an advanced, frequency comb-based optical two-way time-frequency transfer (O-TWTFT) that can successfully synchronize the optical timescales at two sites connected via a time-varying turbulent air path. The link between the two sites is established using either a quadcopter-mounted retroreflector or a swept delay line at speeds up to 24 ms−1. Despite 50-ps breakdown in time-of-flight reciprocity, the sites’ timescales are synchronized to < 1 fs in time deviation. The corresponding sites’ frequencies agree to ~ 10−18 despite 10−7 Doppler shifts. This work demonstrates comb-based O-TWTFT can enable free-space optical networks between airborne or satellite-borne optical clocks for precision navigation, timing and probes of fundamental science.

Numerical investigation on the aerothermoelastic deformation of the hypersonic wing

This paper numerically investigated the aerothermoelastic deformation of the hypersonic wing. An aerothermoelastic analysis framework is developed by using an in-house code and an open source code CalculiX. Aerodynamic load and aerodynamic heat are obtained by employing the in-house code to solve the Reynolds-averaged Navier-Stokes equations. Structural heat transfer analysis and structural static analysis are conducted by adopting the CalculiX module based on the finite element method. The radial basis function interpolation scheme is utilized as a unified method to handle the two-way data transfer and the mesh deformation. The aerothermoelastic analysis framework is validated by several experimental cases. Based on this framework, the aerodynamic heating process, the effects of aerodynamic heating on the characteristics of deformation, and the effects of aerothermoelastic deformation on the aerodynamic performance are investigated in detail. The results indicate that the aerodynamic heating changes the characteristics of the aeroelastic torsion angle. Without aerodynamic heating, the torsion angle increases monotonously along the span direction. With aerodynamic heating, the torsion angle increases at first and then decreases along the span direction. This is mainly due to the severe aerodynamic heating at the leading edge, which causes a larger deformation at the leading edge. In addition, when the aerothermoelastic deformation is taken into consideration, the pressure at the lower surface decreases significantly, and the lift, the drag, the lift-drag ratio and the moment also decrease, especially the moment. The main reason is that the aerothermoelastic deformation reduces the effective angle of attack.

A Dynamic Game Approach for Demand-Side Management: Scheduling Energy Storage with Forecasting Errors

Smart metering infrastructure allows for two-way communication and power transfer. Based on this promising technology, we propose a demand-side management (DSM) scheme for a residential neighbourhood of prosumers. Its core is a discrete time dynamic game to schedule individually owned home energy storage. The system model includes an advanced battery model, local generation of renewable energy, and forecasting errors for demand and generation. We derive a closed-form solution for the best response problem of a player and construct an iterative algorithm to solve the game. Empirical analysis shows exponential convergence towards the Nash equilibrium. A comparison of a DSM scheme with a static game reveals the advantages of the dynamic game approach. We provide an extensive analysis on the influence of the forecasting error on the outcome of the game. A key result demonstrates that our approach is robust even in the worst-case scenario. This grants considerable gains for the utility company organising the DSM scheme and its participants.

Generalized dissipation minimization for generalized flow transfer processes

One of the important research contents of generalized thermodynamic optimization theory is to pursue universality of optimization results. Firstly, on the basis of summarizing and inducing the reasearch contents of dynamic optimizationsfor various irreversible transport processes, including heat transfer, mass transfer, capacitor charging, and resource exchange, this paper defines some physical quantities including generalized potential, generalized force, generalized flow, generalized potenetial capacity, genralized dissipation, generalized dissipation force, and further establishes a generalized therodynamic physical model of a class of generalized flow transfer processes based on generalized thermodynamic optimization theory. The corresponding dynamic optimization problem is formulated. Secondly, the universal optimization result, i.e. the optimality condition as shown in this paper, is obtained by using Euler-Lagrangian method and averaged optimal control theory, respectively. Some new conclusions are obtained based on these universal results. Thirdly, those new results and conclusions are further applied to some special examples, including heat transfer, isothermal throttling, one-way isothermal mass transfer, two-way isothermal equimolar mass transfer, isothermal crystallization, capacitor charging, economic trade processes and so on. Finally, the research idea of “generalized thermodynamic dynamic-optimization” is put forward. The results in this paper enriches and consummates the generalized thermodynamic optimization theory.

Measurement of the impact of turbulence anisoplanatism on precision free-space optical time transfer

Future free-space optical clock networks will require optical links for time and frequency transfer. In many potential realizations of these networks, these links will extend over long distances and will span moving platforms, e.g. ground-to-air or ground-to-satellite. In these cases, the transverse platform motion coupled with spatial variations in atmospheric optical turbulence will lead to a breakdown in the time-of-flight reciprocity upon which optical two-way time-frequency transfer is based. Here, we report experimental measurements of this effect by use of comb-based optical two-way time-frequency transfer over two spatially separated optical links. We find only a modest degradation in the time synchronization and frequency syntonization between two sites, in good agreement with theory. Based on this agreement, we can extrapolate this 2-km result to longer distances, finding only a few-femtosecond timing noise increase due to turbulence for a link from ground to a mid-earth orbit satellite.

Femtosecond optical two-way time-frequency transfer in the presence of motion

Platform motion poses significant challenges to high-precision optical time and frequency transfer. We give a detailed description of these challenges and their solutions in comb-based optical two-way time and frequency transfer (O-TWTFT). Specifically, we discuss the breakdown in reciprocity due to relativity and due to asynchronous sampling, the impact of optical and electrical dispersion, and velocity-dependent transceiver calibration. We present a detailed derivation of the equations governing comb-based O-TWTFT in the presence of motion. We describe the implementation of real-time signal processing algorithms based on these equations and demonstrate active synchronization of two sites over turbulent air paths to below a femtosecond time deviation despite effective velocities of +/-25 m/s, which is the maximum achievable with our physical setup. With the implementation of the time transfer equation derived here, we find no velocity-dependent bias between the synchronized clocks to within at two-sigma statistical uncertainty of 330 attoseconds.

Multifidelity Framework for Modeling Combustion Dynamics

A multifidelity framework oriented toward efficient modeling of combustion dynamics that integrates a reduced-order model (ROM) for the combustion response into the Euler equations is proposed. The ROM is developed from computational fluid dynamics (CFD) simulations of a combusting flow that is periodically forced at the boundaries of a reduced domain. Galerkin’s method is used to reduce the high-order partial differential equations to a low-order ordinary differential equation system via proper orthogonal decomposition eigenbases generated from a reduced-domain dataset. Evaluations of the framework are performed based on parametric studies of a simplified test problem for a model combustor showing distinguishable combustion instability behavior. Two-way information transfer between the ROM and Euler solutions is accomplished by interface matching at the boundaries of the reduced domain. It is shown that accurate predictions require the use of multiple ROMs to account for both upstream- and downstream-traveling perturbations. Characteristic boundary conditions are required at both reduced-domain boundaries to minimize wave reflections and preclude generic unstable responses in the multifidelity model predictions. Comparisons with CFD solutions show the multifidelity model is capable of capturing overall instability trends.

Parameter Optimization of a Bilateral LCC Compensation Structure in Non-contact Energy Transmission

Aiming at the problems of low transmission power and low transmission efficiency in the non-contact energy transmission system, a bilateral LCC compensation network structure under zero voltage turn-on is optimized. Using the fundamental waveform analysis method and the superposition method, the static working characteristics of the system compensation topological equivalent circuit are analyzed, and the system compensation parameter design and ZVS implementation adjustment design are completed. It can work at a constant frequency and reduce switching losses and switching stresses to improve overall system efficiency. Finally, in the system simulation environment, establish a two-way inductive power transfer system for verifying the zero-voltage switching optimized compensation network reliability.

Time synchronization over a free-space optical communication channel

Future high-precision free-space optical (FSO) clock networks will require laser links to transmit time-frequency between sites and, with this information, to synchronize the times across widely separated clocks. FSO communication networks already use laser links between remote sites to transmit high-speed data. Here we repurpose a FSO digital communication system and use it directly for two-way time-frequency transfer. We demonstrate synchronization of the time between two sites separated by a turbulent air path of 4 km using binary-phase-modulated continuous-wave laser light. Under synchronization, the two sites exhibit a fractional frequency deviation below 10−15 at 1500 s averaging time and a time deviation below 1 ps at averaging times of seconds to hours. Over an 8 h period, the peak-to-peak wander is 16 ps. This method should be applicable to future ground-to-space and intra-satellite links and could lead to an improved global navigation and satellite system.

Intense red emission and two-way energy transfer in Sm3+, Eu3+ co-doped NaLa(WO4)2 phosphors

NaLa(WO4)2 phosphors with various Eu3+ and Sm3+ concentrations were prepared via a molten salt method. The structure and luminescent properties of the prepared samples were analyzed by the X-ray diffraction (XRD) and fluorescence spectrophotometer. The results show that the crystal phase of all the prepared samples is single tetragonal crystal structure. The energy transfer type between Eu3+ ions is proved to be the exchange interaction and the electron-phonon coupling is weak. With the increase of the Sm3+ concentration, the energy transfer from Sm3+ to Eu3+ in NaLa(WO4)2:0.15Eu3+,xSm3+ is transformed from Eu3+ to Sm3+, and the mechanism for energy transfer is given.

Mechanical Properties of Innovative, Multi-Layer Composite Laminated Panels

Cross-laminated timber (CLT) possesses both good shape stability and possible two-way force transfer ability due to its crosswise lamination. However, the transverse layers in CLT are prone to rolling shear failure under an out-of-plane load. An innovative multi-layer composite laminated panel (CLP) was developed by combining structural composite lumber (SCL) and dimension lumber to overcome the rolling shear failure while maintaining the high mechanical performance and aesthetic appearance of natural wood. The mechanical properties of 5-layer CLP that consisted of laminated strand lumber (LSL) and dimension lumber with different layups were evaluated by both static and modal tests. The results showed that the shear resistance, bending stiffness, and moment resistance of CLP were up to 143%, 43%, and 87% higher than their counterparts of regular CLT, respectively. The failure modes observed in both shear and bending tests indicated that the use of LSL in transverse layers could eliminate the potential rolling shear failure in CLT. With the lamination properties from components tests as inputs, the validity of shear analogy method was assessed by test results. The mechanical properties can be well predicted by shear analogy method except for the bending moment resistance of CLP and CLT with either rolling failure in the cross layer or tension failure in the bottom layer.

Analysis of the wide area differential correction for BeiDou global satellite navigation system

The regional BeiDou Satellite System, or BDS2, broadcasts a differential correction as Equivalent Satellite Clock Correction to correct both orbit and satellite clock errors. For the global BDS, or BDS3, satellite orbit and clock corrections conforming with RTCA standards will be broadcast to authorized users. The hybrid constellation and regional monitoring network pose challenges for the high precision separation of orbit and satellite clock corrections. Three correction models of kinematic, dynamic and Two-way Satellite Time Frequency Transfer (TWSTFT)-based dynamic were studied to estimate the satellite orbit and clock corrections. The correction accuracy of the three models is compared and analyzed based on the BDS observation data. Results show that the accuracies (root mean square, RMS) of dual-frequency real-time positioning for the three models are about 1.76m, 1.78m and 2.08m respectively, which are comparable with the performance ofWAAS and EGNOS. With dynamic corrections, the precision of Precise Point Positioning (PPP) experiments may reach about 23 cm after convergence.

Direct measurements of two-way wave-particle energy transfer in a collisionless space plasma

Particle acceleration by plasma waves and spontaneous wave generation are fundamental energy and momentum exchange processes in collisionless plasmas. Such wave-particle interactions occur ubiquitously in space. We present ultrafast measurements in Earth's magnetosphere by the Magnetospheric Multiscale spacecraft that enabled quantitative evaluation of energy transfer in interactions associated with electromagnetic ion cyclotron waves. The observed ion distributions are not symmetric around the magnetic field direction but are in phase with the plasma wave fields. The wave-ion phase relations demonstrate that a cyclotron resonance transferred energy from hot protons to waves, which in turn nonresonantly accelerated cold He+ to energies up to ~2 kilo-electron volts. These observations provide direct quantitative evidence for collisionless energy transfer in plasmas between distinct particle populations via wave-particle interactions.

An enhanced SSD with feature fusion and visual reasoning for object detection

Single Shot Multibox Detector (SSD) is one of the top performing object detection algorithms in terms of both accuracy and speed. SSD achieves impressive performance on various datasets by using different output layers for object detection. However, each layer in the feature pyramid is used independently, and SSD considers only the fine-grained details of the objects but ignores the context surrounding objects. In this paper, we proposed an enhanced SSD, called ESSD, that improved the performance of the conventional SSD by fusing feature maps of different output layers, instead of growing layers close to the input data. Our method used two-way transfer of feature information and feature fusion to enhance the network. To assist further with object detection, we proposed a visual reasoning method that utilized fully the relationships between objects instead of using only the features of the objects themselves. This addition of visual reasoning proved very effective for detecting objects that are too small or have small features. To evaluate the proposed ESSD, we trained the model with VOC2007 and VOC2012 training sets and evaluated the performance on the Pascal VOC2007 test set. For $$300 \times 300$$ input, ESSD achieved 79.2% mean average precision (mAP) at 52.0 frames per second (FPS), and for $$512 \times 512$$ input, this approach achieved 82.4% mAP at 18.6 FPS. These results demonstrated that our proposed method can achieve state-of-the-art mAP, which is a better result than provided by the conventional SSD and other advanced detectors.

The on-line coupled atmospheric chemistry model system MECO(n) – Part 5: Expanding the Multi-Model-Driver (MMD v2.0) for 2-way data exchange including data interpolation via GRID (v1.0)

Abstract. As part of the Modular Earth Submodel System (MESSy), the Multi-Model-Driver (MMD v1.0) was developed to couple online the regional Consortium for Small-scale Modeling (COSMO) model into a driving model, which can be either the regional COSMO model or the global European Centre Hamburg general circulation model (ECHAM) (see Part 2 of the model documentation). The coupled system is called MECO(n), i.e., MESSy-fied ECHAM and COSMO models nested n times. In this article, which is part of the model documentation of the MECO(n) system, the second generation of MMD is introduced. MMD comprises the message-passing infrastructure required for the parallel execution (multiple programme multiple data, MPMD) of different models and the communication of the individual model instances, i.e. between the driving and the driven models. Initially, the MMD library was developed for a one-way coupling between the global chemistry–climate ECHAM/MESSy atmospheric chemistry (EMAC) model and an arbitrary number of (optionally cascaded) instances of the regional chemistry–climate model COSMO/MESSy. Thus, MMD (v1.0) provided only functions for unidirectional data transfer, i.e. from the larger-scale to the smaller-scale models.Soon, extended applications requiring data transfer from the small-scale model back to the larger-scale model became of interest. For instance, the original fields of the larger-scale model can directly be compared to the upscaled small-scale fields to analyse the improvements gained through the small-scale calculations, after the results are upscaled. Moreover, the fields originating from the two different models might be fed into the same diagnostic tool, e.g. the online calculation of the radiative forcing calculated consistently with the same radiation scheme. Last but not least, enabling the two-way data transfer between two models is the first important step on the way to a fully dynamical and chemical two-way coupling of the various model instances.In MMD (v1.0), interpolation between the base model grids is performed via the COSMO preprocessing tool INT2LM, which was implemented into the MMD submodel for online interpolation, specifically for mapping onto the rotated COSMO grid. A more flexible algorithm is required for the backward mapping. Thus, MMD (v2.0) uses the new MESSy submodel GRID for the generalised definition of arbitrary grids and for the transformation of data between them.In this article, we explain the basics of the MMD expansion and the newly developed generic MESSy submodel GRID (v1.0) and show some examples of the abovementioned applications.

Urban Parks in the Twentieth Century

Abstract This paper summarises the history of urban parks, primarily in the United States and in western Europe, throughout the twentieth century and in the early twenty-first century. In terms of park design this shows a transition from early pastoral models, via form-driven Beaux-Arts and City Beautiful models, to function-driven modernist approaches to park design and, latterly, ecologically-driven approaches that treat parks as elements of urban green infrastructure. These transitions demonstrate the influence of the zeitgeist in the two-way transfer of approaches to park design between the two continents. These approaches to the design of urban parks reflect changes in the social and political purposes for which they were intended, evolving from being seen as escapes from infernal cities, then as places for active physical recreation (including the preparation of young men for war) and latterly as principal components of urban open space systems. Equally, the importance attached to these evolving purposes has been reflected in the public funds made available for their creation and maintenance, with post World War II suburbanisation leading to severe decline in the condition and facilities in parks in both continents. Latterly urban densification has prompted higher levels of private and central government funding, while local government funding has fallen as a result of priority being given to statutory services.

Comparing Optical Oscillators across the Air to Milliradians in Phase and 10^{-17} in Frequency.

We demonstrate carrier-phase optical two-way time-frequency transfer (carrier-phase OTWTFT) through the two-way exchange of frequency comb pulses. Carrier-phase OTWTFT achieves frequency comparisons with a residual instability of 1.2×10^{-17} at 1s across a turbulent 4-km free space link, surpassing previous OTWTFT by 10-20 times and enabling future high-precision optical clock networks. Furthermore, by exploiting the carrier phase, this approach is able to continuously track changes in the relative optical phase of distant optical oscillators to 9mrad (7as) at 1s averaging, effectively extending optical phase coherence over a broad spatial network for applications such as correlated spectroscopy between distant atomic clocks.

Enabling Small Medium Enterprises (SMEs) to improve their potential through the Teaching Factory paradigm

In the last decade, Teaching Factories, which enable a two-way knowledge transfer in manufacturing education, have been built up in industry and academia. Such initiatives from local to worldwide level help both parties to mutually benefit. This paper introduces a framework for the delivery of industrial learning and training to young engineers creating at the same time the prerequisites which enable SMEs to explore new technologies through the Teaching Factory paradigm. In particular, through this framework, participants will be the receivers of valuable knowledge and will be able to cope with the increasing industrial requirements of the factories of the future. Following this framework, a win-win collaboration is going to be achieved with the involved parties, academia and industry, to benefit reciprocally. Finally, the proposed framework is validated in a use case from an equipment manufacturing industry and the presented results demonstrate the potential of incorporating Small Medium Enterprises (SMEs) in the Teaching Factory paradigm.

Encountering the pedagogy of live and interactive architectural projects

&lt;p class="Normale1"&gt;The use of the word “live” as a prefix for a project, is a thought-provoking, and perplexing concept; does one assume that all other projects are dead?&lt;br /&gt;Or is it that "(a)live," in the studio build paradigm, is about the currency and value of the moment? Or is it that one is operating outside of normative architectural academia, and is therefore (a)live?&lt;br /&gt;Untangling the meta meaning of the verb “live” and then juxtaposing it with the word “interactive” could draw the reader to the conclusion that we are talking about a non-momentary or continuous two-way transfer of information – often as not between the student, the lecturing staff and external agencies (in many cases real clients). It is this existence between the borderland of academia and practice that this chapter hopes to unpack and clarify.&lt;/p&gt;&lt;p class="Normale1"&gt;This article is an introduction to contents of Chapter II.&lt;/p&gt;

Low-loss reciprocal optical terminals for two-way time-frequency transfer.

We present the design and performance of a low-cost, reciprocal, compact free-space terminal employing tip/tilt pointing compensation that enables optical two-way time-frequency transfer over free-space links across the turbulent atmosphere. The insertion loss of the terminals is ∼1.5 dB with total link losses of 15dB, 24dB, and 50dB across horizontal, turbulent 2-km, 4-km, and 12-km links, respectively. The effects of turbulence on pointing control and aperture size, and their influence on the terminal design, are discussed.