344 research outputs found
Switching Control Strategy for Greenhouse Temperature-Humidity System Based on Prediction Modeling: A Simulation Study
It is difficult to achieve coordination control of multiple facilities that are driven by on-off actuators in a greenhouse, especially when there is more than one indoor environmental factor to consider at the same time. With the consideration of indoor air temperature and relative humidity, we propose a switching control strategy based on prediction modeling. The operation of the greenhouse system was divided into several modes according to the on-off control characteristics of the available facilities. Then, a switching diagram was designed according to the relationship between the indoor air temperature and humidity and their setting ranges. When the two indoor environmental factors reach their upper or lower limits, IARX models are used to predict them over a specified horizon for each optional mode respectively. Mode switching is carried out based on prediction results. The switching control strategy was simulated based on a mechanistic model of the greenhouse microclimate. The results show that the facilities can be coordinated very well by the proposed control strategy and it is easy to implement. The control strategy is still applicative when more facilities or more indoor environmental factors need to be taken into account
Water, rather than temperature, dominantly impacts how soil fauna affect dissolved carbon and nitrogen release from fresh litter during early litter decomposition
Longstanding observations suggest that dissolved materials are lost from fresh litter through leaching, but the role of soil fauna in controlling this process has been poorly documented. In this study, a litterbag experiment employing litterbags with different mesh sizes (3 mm to permit soil fauna access and 0.04 mm to exclude fauna access) was conducted in three habitats (arid valley, ecotone and subalpine forest) with changes in climate and vegetation types to evaluate the effects of soil fauna on the concentrations of dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) during the first year of decomposition. The results showed that the individual density and community abundance of soil fauna greatly varied among these habitats, but Prostigmata, Isotomidae and Oribatida were the dominant soil invertebrates. At the end of the experiment, the mass remaining of foliar litter ranged from 58% for shrub litter to 77% for birch litter, and the DOC and TDN concentrations decreased to 54%-85% and increased to 34%-269%, respectively, when soil fauna were not present. The effects of soil fauna on the concentrations of both DOC and TDN in foliar litter were greater in the subalpine forest (wetter but colder) during the winter and in the arid valley (warmer but drier) during the growing season, and this effect was positively correlated with water content. Moreover, the effects of fauna on DOC and TDN concentrations were greater for high-quality litter and were related to the C/N ratio. These results suggest that water, rather than temperature, dominates how fauna affect the release of dissolved substances from fresh litter
Assessment of Long-Term Watershed Management on Reservoir Phosphorus Concentrations and Export Fluxes.
Source water nutrient management to prevent eutrophication requires critical strategies to reduce watershed phosphorus (P) loadings. Shanxi Drinking-Water Source Area (SDWSA) in eastern China experienced severe water quality deterioration before 2010, but showed considerable improvement following application of several watershed management actions to reduce P. This paper assessed the changes in total phosphorus (TP) concentrations and fluxes at the SDWSA outlet relative to watershed anthropogenic P sources during 2005ā»2016. Overall anthropogenic P inputs decreased by 21.5% over the study period. Domestic sewage, livestock, and fertilizer accounted for (mean Ā± SD) 18.4 Ā± 0.6%, 30.1 Ā± 1.9%, and 51.5 Ā± 1.5% of total anthropogenic P inputs during 2005ā»2010, compared to 24.3 Ā± 2.7%, 8.8 Ā± 10.7%, and 66.9 Ā± 8.0% for the 2011ā»2016 period, respectively. Annual average TP concentrations in SDWSA decreased from 0.041 Ā± 0.019 mg/L in 2009 to 0.025 Ā± 0.013 mg/L in 2016, a total decrease of 38.2%. Annual P flux exported from SDWSA decreased from 0.46 Ā± 0.04 kg P/(haĀ·a) in 2010 to 0.25 Ā± 0.02 kg P/(haĀ·a) in 2016, a decrease of 44.9%. The success in reducing TP concentrations was mainly due to the development of domestic sewage/refuse collection/treatment and improved livestock management. These P management practices have prevented harmful algal blooms, providing for safe drinking water
Non-Transferable Proxy Re-Encryption
Proxy re-encryption (PRE) allows a semi-trusted proxy to transform a ciphertext for Alice into a ciphertext of the same message for Bob. The traditional security notion of PRE focuses on preventing the proxy with the re-encryption key learning anything about the encrypted messages. However, such a basic security requirement is clearly not enough for many scenarios where the proxy can collude with Bob. A desirable security goal is therefore to prevent a malicious proxy colluding with Bob to re-delegate Aliceās decryption right. In 2005, Ateniese, Fu, Green and Hohenberger first proposed this intriguing problem called non-transferability, in the sense that the only way for Bob to transfer Aliceās decryption capability is to expose his own secret key. It captures the notion that Bob cannot collude with the proxy and transfer Aliceās decryption right without compromising his own decryption capability. However, over the last decade, no solutions have achieved this property.
In this paper, we positively resolve this open problem. In particular, we give the first construction of nontransferable proxy re-encryption where the attacker is allowed to obtain one pair of keys consisting of Bobās secret key and the corresponding re-encryption key. Using indistinguishability obfuscation and k-unforgeable authentication as main tools, our scheme is provably secure in the standard model. The essential idea behind our approach is to allow Bobās secret key to be evoked in the process of decrypting Aliceās ciphertext while hiding the fact that only Bob could decrypt it by the obfuscated program. In addition, we also show a negative result: a CPA secure proxy re-encryption scheme with āerror-freenessā property cannot be non-transferable
Dumbo-NG: Fast Asynchronous BFT Consensus with Throughput-Oblivious Latency
Despite recent progresses of practical asynchronous Byzantine fault tolerant
(BFT) consensus, the state-of-the-art designs still suffer from suboptimal
performance. Particularly, to obtain maximum throughput, most existing
protocols with guaranteed linear amortized communication complexity require
each participating node to broadcast a huge batch of transactions, which
dramatically sacrifices latency. Worse still, the f slowest nodes' broadcasts
might never be agreed to output and thus can be censored (where f is the number
of faults). Implementable mitigation to the threat either uses computationally
costly threshold encryption or incurs communication blow-up, thus causing
further efficiency issues.
We present Dumbo-NG, a novel asynchronous BFT consensus (atomic broadcast) to
solve the remaining practical issues. Its technical core is a non-trivial
direct reduction from asynchronous atomic broadcast to multi-valued validated
Byzantine agreement (MVBA) with quality property. Most interestingly, the new
protocol structure empowers completely concurrent execution of transaction
dissemination and asynchronous agreement. This brings about two benefits: (i)
the throughput-latency tension is resolved to approach peak throughput with
minimal increase in latency; (ii) the transactions broadcasted by any honest
node can be agreed to output, thus conquering the censorship threat with no
extra cost.
We implement Dumbo-NG and compare it to the state-of-the-art asynchronous BFT
with guaranteed censorship resilience including Dumbo (CCS'20) and
Speeding-Dumbo (NDSS'22). We also apply the techniques from Speeding-Dumbo to
DispersedLedger (NSDI'22) and obtain an improved variant of DispersedLedger
called sDumbo-DL for comprehensive comparison. Extensive experiments reveal:
Dumbo-NG realizes better peak throughput performance and its latency can almost
remain stable when throughput grows
Identity Based Threshold Proxy Signature
Identity-based (ID-based) public key cryptosystem can be a good
alternative for certificate-based public key setting, especially
when efficient key management and moderate security are required.
In a threshold proxy signature scheme, the original signer
delegates the power of signing messages to a designated proxy
group of members. Any or more proxy signers of the group
can cooperatively issue a proxy signature on behalf of the
original signer, but or less proxy signers cannot. In this
paper, we present an ID-based threshold proxy signature scheme
using bilinear pairings. We show the scheme satisfies all security
requirements in the random oracle model. To the best of authors\u27
knowledge, our scheme is the first ID-based threshold proxy
signature scheme
Efficient Asynchronous Byzantine Agreement without Private Setups
Efficient asynchronous Byzantine agreement (BA) protocols were mostly studied
with private setups, e.g., pre-setup threshold cryptosystem. Challenges remain
to reduce the large communication in the absence of such setups. Recently,
Abraham et al. (PODC'21) presented the first asynchronous validated BA (VBA)
with expected messages and rounds, relying on only public key
infrastructure (PKI) setup, but the design still costs
bits. Here is the number of parties, and is a cryptographic
security parameter.
In this paper, we reduce the communication of private-setup free asynchronous
BA to expected bits. At the core of our design, we give a
systematic treatment of common randomness protocols in the asynchronous
network, and proceed as: - We give an efficient reasonably fair common coin
protocol in the asynchronous setting with only PKI setup. It costs only
bits and rounds, and ensures that with at least 1/3
probability, all honest parties can output a common bit that is as if randomly
flipped. This directly renders more efficient private-setup free asynchronous
binary agreement (ABA) with expected bits and rounds. -
Then, we lift our common coin to attain perfect agreement by using a single
ABA. This gives us a reasonably fair random leader election protocol with
expected communication and expected constant rounds. It is
pluggable in all existing VBA protocols (e.g., Cachin et al., CRYPTO'01;
Abraham et al., PODC'19; Lu et al., PODC'20) to remove the needed private setup
or distributed key generation (DKG). As such, the communication of
private-setup free VBA is reduced to expected bits while
preserving fast termination in expected rounds
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