2,407 research outputs found
Debiasing Conditional Stochastic Optimization
In this paper, we study the conditional stochastic optimization (CSO) problem
which covers a variety of applications including portfolio selection,
reinforcement learning, robust learning, causal inference, etc. The
sample-averaged gradient of the CSO objective is biased due to its nested
structure and therefore requires a high sample complexity to reach convergence.
We introduce a general stochastic extrapolation technique that effectively
reduces the bias. We show that for nonconvex smooth objectives, combining this
extrapolation with variance reduction techniques can achieve a significantly
better sample complexity than existing bounds. We also develop new algorithms
for the finite-sum variant of CSO that also significantly improve upon existing
results. Finally, we believe that our debiasing technique could be an
interesting tool applicable to other stochastic optimization problems too
Using Context and Interactions to Verify User-Intended Network Requests
Client-side malware can attack users by tampering with applications or user
interfaces to generate requests that users did not intend. We propose Verified
Intention (VInt), which ensures a network request, as received by a service, is
user-intended. VInt is based on "seeing what the user sees" (context). VInt
screenshots the user interface as the user interacts with a security-sensitive
form. There are two main components. First, VInt ensures output integrity and
authenticity by validating the context, ensuring the user sees correctly
rendered information. Second, VInt extracts user-intended inputs from the
on-screen user-provided inputs, with the assumption that a human user checks
what they entered. Using the user-intended inputs, VInt deems a request to be
user-intended if the request is generated properly from the user-intended
inputs while the user is shown the correct information. VInt is implemented
using image analysis and Optical Character Recognition (OCR). Our evaluation
shows that VInt is accurate and efficient
COLA: Decentralized Linear Learning
Decentralized machine learning is a promising emerging paradigm in view of
global challenges of data ownership and privacy. We consider learning of linear
classification and regression models, in the setting where the training data is
decentralized over many user devices, and the learning algorithm must run
on-device, on an arbitrary communication network, without a central
coordinator. We propose COLA, a new decentralized training algorithm with
strong theoretical guarantees and superior practical performance. Our framework
overcomes many limitations of existing methods, and achieves communication
efficiency, scalability, elasticity as well as resilience to changes in data
and participating devices
Byzantine-Robust Learning on Heterogeneous Datasets via Bucketing
In Byzantine robust distributed or federated learning, a central server wants
to train a machine learning model over data distributed across multiple
workers. However, a fraction of these workers may deviate from the prescribed
algorithm and send arbitrary messages. While this problem has received
significant attention recently, most current defenses assume that the workers
have identical data. For realistic cases when the data across workers are
heterogeneous (non-iid), we design new attacks which circumvent current
defenses, leading to significant loss of performance. We then propose a simple
bucketing scheme that adapts existing robust algorithms to heterogeneous
datasets at a negligible computational cost. We also theoretically and
experimentally validate our approach, showing that combining bucketing with
existing robust algorithms is effective against challenging attacks. Our work
is the first to establish guaranteed convergence for the non-iid Byzantine
robust problem under realistic assumptions.Comment: v4 is a major overhaul of the paper and has significantly stronger
theory and experiment
Braided stent-assisted coil embolization versus laser engraved stent-assisted coil embolization in patients with unruptured complex intracranial aneurysms
Purposes: Braided and laser-cut stents both are efficacious and safe for coiling intracranial aneurysms. The study aimed to compare outcomes following braided stent-assisted coil embolization versus laser engraved stent-assisted coil embolization in 266 patients who were diagnosed with unruptured intracranial aneurysms of different types and locations.
Methods: Patients with unruptured complex intracranial aneurysms underwent braided (BSE cohort, n = 125) or laser engraved (LSE cohort, n = 141) stent-assisted embolization.
Results: The deployment success rate was higher for patients of the LSE cohort than those of the BSE cohort (140 [99%] vs. 117 [94%], p = 0.0142). Seventy-one (fifty-seven percentages) and 73 (52%) were coil embolization procedure success rates of the BSE and the LSE cohorts. Periprocedural intracranial hemorrhage was higher in patients of the BSE cohort than those of the LSE cohort (8 [6%] vs. 1 [1%], p = 0.0142). Four (three percentages) patients from the LSE cohort and 3 (2%) patients from the BSE cohort had in-stent thrombosis during embolization. Permanent morbidities were higher in patients of the LSE cohort than those of the BSE cohort (8 [6%] vs. 1 [1%], p = 0.0389). Higher successful procedures (76% vs. 68%) and fewer postprocedural intracranial hemorrhage (0% vs. 5%) and mortality (0% vs. 5%) were reported for patients of the BSE cohort in posterior circulation aneurysmal location than those of the LSE cohort. Laser engraved stent has fewer problems with deployment and may have better periprocedural and follow-up outcomes after embolization.
Conclusions: Braided stent-assisted embolization should be preferred when the aneurysm is present in the posterior circulation
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