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1. Understanding the Key Factors for Photoinduced Radical Generation in Crystalline Triphenylamines Using Experiment and Machine Learning

   https://doi.org/10.1021/acs.jpcc.4c03579  

   Wijesekera, Gamage_Isuri P; Gbadamosi, Fahidat A; Hossain, Muhammad Saddam; Patra, Abhilash; Sutton, Christopher; Shimizu, Linda S (October 2024, The Journal of Physical Chemistry C)

   In this study, we combine experiments, calculated properties, and machine learning (ML) to design new triphenylamine-based (TPA) molecules that have a high photoinduced radical (PIR) generation in crystals. A dataset of 34 crystal structures was extracted from the Cambridge Crystallographic Data Centre. Eighteen structures with experimentally reported PIR values from 0 to 0.85% were used to build an ML model trained using Random Forest that achieves an average leave-one-out test set error of 0.173% PIR. The ML model was used to screen the remaining 16 compounds, of which 4 were selected and sub-sequently compared with the experimentally measured PIR%. The predicted PIR% demonstrated good agreement with the measured values of TPA bis-urea macrocycles host-guest complexes and non-macrocyclic compounds of TPAs. Examining a broad set of molecular architectures/scaffolds allows for investigating the structural and electronic properties that lead to high PIR generation. We found very different trends for macrocycles, linear TPAs, and mono TPAs, where mono TPAs consist-ently have the lowest PIR generation. Macrocycles tend to have the highest PIR generation, especially for systems with ben-zene and fluorobenzene guests. Although linear analogs overall perform worse than macrocycles, they display clear trends with increasing excited-state dipole moment, oscillator strength and electron-hole covariance, while decreasing ionization potential and interatomic distance are generally correlated with higher PIRs. What is consistently observed is that higher PIRs are seen for brominated analogs. Our study, therefore, provides guidelines for future design strategies of TPAs for PIR generation. 

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2. On the Capacity of Leaky Private Information Retrieval

   https://doi.org/10.1109/ISIT.2019.8849676  

   Samy, Islam; Tandon, Ravi; Lazos, Loukas (July 2019, 2019 IEEE International Symposium on Information Theory (ISIT))

   Private information retrieval (PIR) allows users to retrieve data from databases without revealing the identity of that data. An extensive body of works has investigated efficient schemes to achieve computational and information-theoretic privacy. The latter guarantees that no information is revealed to the databases, irrespective of their computational power. Although information-theoretic PIR (IT-PIR) provides a strong privacy guarantee, it can be too taxing for certain applications. In this paper, we initiate the study of leaky private information retrieval (L-PIR), where a bounded amount of privacy leakage is allowed and measured through a parameter ε. The classical IT-PIR formulation is obtained by setting ε = 0, and for ε > 0, we explore the opportunities offered for reducing the download cost. We derive new upper and lower bounds on the download cost of L-PIR for any arbitrary ε, any number of messages K, and for N = 2 databases. 

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3. Heterogeneous Private Information Retrieval

   https://doi.org/10.14722/ndss.2020.24363  

   Mozaffari, Hamid; Houmansadr, Amir (January 2020, Network and Distributed Systems Security (NDSS) Symposium 2020)

   Private information retrieval (PIR) enables clients to query and retrieve data from untrusted servers without the untrusted servers learning which data was retrieved. In this paper, we present a new class of multi-server PIR protocols, which we call heterogeneous PIR (HPIR). In such multi-server PIR protocols, the computation and communication overheads imposed on the PIR servers are non-uniform, i.e., some servers handle higher computation/communication burdens than the others. This enables heterogeneous PIR protocols to be suitable for a range of new PIR applications. What enables us to enforce such heterogeneity is a unique PIR-tailored secret sharing algorithm that we leverage in building our PIR protocol. We have implemented our HPIR protocol and evaluated its performance in comparison with regular (i.e., homogenous) PIR protocols. Our evaluations demonstrate that a querying client can trade off the computation and communication loads of the (heterogeneous) PIR servers by adjusting some parameters. For example in a two-server scenario with a heterogeneity degree of 4/1, to retrieve a 456KB file from a 0.2GB database, the rich (i.e., resourceful) PIR server will do 1.1 seconds worth of computation compared to 0.3 seconds by the poor (resource-constrained) PIR server; this is while each of the servers would do the same 1 seconds of computation in a homogeneous setting. Also, for this given example, our HPIR protocol will impose a 912KB communication bandwidth on the rich server compared to 228KB on the poor server (by contrast to 456KB overheads on each of the servers for a traditional homogeneous design). 

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4. Probabilistic Interpolation Recoder for Energy-Error-Product Efficient DBNs with p-bit Devices

   https://doi.org/10.1109/TETC.2020.2965079  

   Pourmeidani, Hossein; Sheikhfaal, Shadi; Zand, Ramtin; DeMara, Ronald F. (January 2020, IEEE Transactions on Emerging Topics in Computing)

   In this paper, a probabilistic interpolation recoder (PIR) circuit is developed for deep belief networks (DBNs) with probabilistic spin logic (p-bit)-based neurons. To verify the functionality and evaluate the performance of the PIRs, we have implemented a 784 × 200 × 10 DBN circuit in SPICE for a pattern recognition application using the MNIST dataset. The PIR circuits are leveraged in the last hidden layer to interpolate the probabilistic output of the neurons, which are representing different output classes, through sampling the p-bit’s output values and then counting them in a defined sampling time window. The PIR circuit is proposed as an alternative for conventional interpolation methods which were based on using a resistor capacitor tank to integrate each neuron’s output, followed by an analog-to-digital converter to generate the digital output. The circuit simulation results of PIR circuit exhibit at least 54%, 81%, and 78% reductions in power, energy, and energy-error-product, respectively, compared to previous techniques, without using any of the area-consuming analog components in the interpolation circuit. In addition, PIR circuits provide an inherent single stuck at fault tolerant feature to mitigate both transient and permanent faults at the circuit’s output. Reliability properties of the PIR circuits for single stuck-at faults are shown to be enhanced relative to conventional interpolation without requiring hardware redundancy. 

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5. The Capacity of Uncoded Storage Constrained PIR

   https://doi.org/10.1109/ISIT.2018.8437729  

   Attia, Mohamed Adel; Kumar, Deepak; Tandon, Ravi (June 2018, 2018 IEEE International Symposium on Information Theory (ISIT))

   Private information retrieval (PIR) allows a user to retrieve a desired message out of K possible messages from N databases (DBs) without revealing the identity of the desired message. In this work, we consider the problem of PIR from uncoded storage constrained DBs. Each DB has a storage capacity of μKL bits, where L is the size of each message in bits, and μ ∈ [1/N, 1] is the normalized storage. In the storage constrained PIR problem, there are two key challenges: a) construction of communication efficient schemes through storage content design at each DB that allow download efficient PIR; and b characterizing the optimal download cost via information-theoretic lower bounds. The novel aspect of this work is to characterize the optimum download cost of PIR with storage constrained DBs for any value of storage. In particular, for any (N, K), we show that the optimal tradeoff between storage (μ) and the download cost (D(μ)) is given by the lower convex hull of the pairs ([t/N](1+[1/t]+[1/(t 2 )]+...+[1/(t K-1 )])) for t = 1,2, ..., N. The main contribution of this paper is the converse proof, i.e., obtaining lower bounds on the download cost for PIR as a function of the available storage. 

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