2,456 research outputs found
Transmit Power Allocation for BER Performance Improvement in Multicarrier Systems
This paper was presented
in part at the IEEE International Symposium on Personal, Indoor, and Mobile
Radio Communications, Lisbon, Portugal, September 2002.In a multicarrier system, transmit power allocation
over different subchannels is an effective means of improving the
performance. We develop the optimal transmit power allocation
scheme to improve bit-error rate (BER) performance in a multicarrier
system with diversity reception. A simple suboptimal
scheme is also derived from the optimal one, and an asymptotic
case referred to as the equal-signal-to-noise ratio scheme
is discussed. Numerical results show that the optimal and suboptimal
power allocation schemes significantly outperform the
equal power allocation scheme. The effects of the modulation
level, the number of receiving antennas, and the number of
subchannels on the BER performance are also investigated
Transmit Power Allocation for Successive Interference Cancellation in Multicode MIMO Systems
Paper approved by X. Wang, the Editor for Multiuser Detection and
Equalization of the IEEE Communications Society. Manuscript received June
10, 2005; revised November 2, 2006 and July 23, 2007. This paper was
presented in part at the IEEE International Conference on Communications,
Seoul, Korea, May 2005.Multiple-input multiple-output (MIMO) system
with multicode transmission can provide high speed data services
by transmitting independent parallel substreams from multiple
antennas and through multicode channelization. In this paper,
we first introduce an iterative two-stage successive interference
cancellation (SIC) detection scheme for a multicode MIMO
system. The proposed technique cancels the interference signals
successively in the space domain followed by the code domain.
Next, we develop various transmit power allocation schemes over
different data substreams for the proposed detection process to
improve error rate performance. The joint transmit power allocation
is derived to make the post-detection signal-to-interferenceplus-
noise ratio (SINR) become the same for all substreams
in both the space and code domains. As a computationally
efficient scheme, we propose a two-stage power allocation scheme,
which allocates the total transmit power to the substreams in
the code domain at the first stage, and allocates this code
domain power to the substreams in the space domain at the
second stage. Furthermore, variable and constant power ratio
(PR) schemes are derived to reduce the feedback overhead. In
particular, the constant PR scheme utilizes the transmit power
ratio determined by the long-term statistical properties of the
fading channel amplitudes, and achieves significantly reduced
feedback rate. Numerical results show that the proposed transmit
power allocation schemes for the two-stage SIC significantly
outperform the equal power allocation scheme
Statistical Multimode Transmit Antenna Selection for Limited Feedback MIMO Systems
This paper was
presented in part at the Asia-Pacific Conference on Communications, Busan,
Korea, August 2006.In a wireless multiple-input multiple-output
(MIMO) system, transmit antenna selection is an effective
means of achieving good performance with low complexity. We
consider spatial multiplexing with linear receivers, and equal
power and equal rate allocation over different selected transmit
antennas in order to reduce feedback overhead. Under these
constraints, we address the problem of statistical multimode
transmit antenna subset selection to improve the capacity
of spatially correlated MIMO fading channels. In particular,
we first derive an analytical closed-form expression for the
expectation of the lower bound on the capacity using the
smallest eigenvalue distribution of a Wishart matrix. Then,
we propose a transmit antenna subset selection criterion of
maximizing this average lower-bound capacity
CT Examinations for COVID-19: A Systematic Review of Protocols, Radiation Dose, and Numbers Needed to Diagnose and Predict
Purpose
Although chest CT has been discussed as a first-line test for coronavirus disease 2019 (COVID-19), little research has explored the implications of CT exposure in the population. To review chest CT protocols and radiation doses in COVID-19 publications and explore the number needed to diagnose (NND) and the number needed to predict (NNP) if CT is used as a first-line test.
Materials and Methods
We searched nine highly cited radiology journals to identify studies discussing the CT-based diagnosis of COVID-19 pneumonia. Study-level information on the CT protocol and radiation dose was collected, and the doses were compared with each national diagnostic reference level (DRL). The NND and NNP, which depends on the test positive rate (TPR), were calculated, given a CT sensitivity of 94% (95% confidence interval [CI]: 91%–96%) and specificity of 37% (95% CI: 26%–50%), and applied to the early outbreak in Wuhan, New York, and Italy.
Results
From 86 studies, the CT protocol and radiation dose were reported in 81 (94.2%) and 17 studies (19.8%), respectively. Low-dose chest CT was used more than twice as often as standard-dose chest CT (39.5% vs.18.6%), while the remaining studies (44.2%) did not provide relevant information. The radiation doses were lower than the national DRLs in 15 of the 17 studies (88.2%) that reported doses. The NND was 3.2 scans (95% CI: 2.2–6.0). The NNPs at TPRs of 50%, 25%, 10%, and 5% were 2.2, 3.6, 8.0, 15.5 scans, respectively. In Wuhan, 35418 (TPR, 58%; 95% CI: 27710–56755) to 44840 (TPR, 38%; 95% CI: 35161–68164) individuals were estimated to have undergone CT examinations to diagnose 17365 patients. During the early surge in New York and Italy, daily NNDs changed up to 5.4 and 10.9 times, respectively, within 10 weeks.
Conclusion
Low-dose CT protocols were described in less than half of COVID-19 publications, and radiation doses were frequently lacking. The number of populations involved in a first-line diagnostic CT test could vary dynamically according to daily TPR; therefore, caution is required in future planning
Forest Decline Under Progress in the Urban Forest of Seoul, Central Korea
Vegetation in the urban area showed not only a difference in species composition but also lower diversity compared with that of the natural area. Successional trend was normal in natural area, but that in urban areas showed a retrogressive pattern. Korean mountain ash (Sorbus alnifolia (Siebold & Zucc.) K.Koch), a shade intolerant species, dominated such a retrogressive succession. The vegetation decline is due to changes of mesoclimate and soil properties that imbalanced distribution of green space induced as the result of urbanization. In recent years, new environmental stress due to climate change is imposed additively to this forest decline. Drought is the very environmental stress. Drought-induced plant damage started from withering of leaves of plants introduced for landscaping in the urban area. Over time, branches died and death of the whole plant body followed. In particular, damage of Korean mountain ash, the product of retrogressive succession, was remarkable. As retrogressive succession has already progressed much, thus such phenomenon could be recognized as crisis of urban forest
Acanthopanax koreanum Fruit Waste Inhibits Lipopolysaccharide-Induced Production of Nitric Oxide and Prostaglandin E2 in RAW 264.7 Macrophages
The Acanthopanax koreanum fruit is a popular fruit in Jeju Island, but the byproducts of the alcoholic beverage prepared using this fruit are major agricultural wastes. The fermentability of this waste causes many economic and environmental problems. Therefore, we investigated the suitability of using A. koreanum fruit waste (AFW) as a source of antiinflammatory agents. AFWs were extracted with 80% EtOH. The ethanolic extract was then successively partitioned with hexane, CH2Cl2, EtOAc, BuOH, and water. The results indicate that the CH2Cl2 fraction (100 μg/mL) of AFW inhibited the LPS-induced nitric oxide (NO) and prostaglandin E2 (PGE2) production in RAW 264.7 cells by 79.6% and 39.7%, respectively. These inhibitory effects of the CH2Cl2 fraction of AFWs were accompanied by decreases in the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) proteins and iNOS and COX-2 mRNA in a dose-dependent pattern. The CH2Cl2 fraction of AFWs also prevented degradation of IκB-α in a dose-dependent manner. Ursolic acid was identified as major compound present in AFW, and CH2Cl2 extracts by high performance liquid chromatography (HPLC). Furthermore using pure ursolic acid as standard and by HPLC, AFW and CH2Cl2 extracts was found to contain 1.58 mg/g and 1.75 mg/g, respectively. Moreover, we tested the potential application of AFW extracts as a cosmetic material by performing human skin primary irritation tests. In these tests, AFW extracts did not induce any adverse reactions. Based on these results, we suggest that AFW extracts be considered possible anti-inflammatory candidates for topical application
Comparison of Conventional Excision via a Sublabial Approach and Transnasal Marsupialization for the Treatment of Nasolabial Cysts: A Prospective Randomized Study
ObjectivesSurgical excision via a sublabial approach is considered the standard treatment for nasolabial cysts. Although transnasal marsupialization has been proposed as an alternative method, no prospective study has compared the effectiveness of these techniques. We thus compared the surgical procedure, operating time, postoperative pain, complications, and recurrence rate between the two surgical methods.MethodsTwenty patients diagnosed with nasolabial cysts were allocated randomly into two groups according to the surgical technique. In the sublabial approach group, the cysts were excised completely using a sublabial approach, while in the transnasal marsupialization group, the cysts were marsupialized transnasally under the guidance of nasal endoscopes. The pure operating time was measured and postoperative pain was evaluated using a visual analog scale. Complications after the procedure were assessed and recurrence was determined according to the clinical symptoms and postoperative radiologic findings.ResultsThe transnasal marsupialization group had significantly shorter operating times, less postoperative pain, lower complication rates, and shorter duration of side effects than the sublabial approach group. No recurrence occurred in either group after a 1-yr follow-up period.ConclusionAlthough both methods are effective for treating nasolabial cysts, the transnasal marsupialization of nasolabial cysts has many benefits over the conventional sublabial approach. Therefore, we propose that transnasal marsupialization be the treatment of choice for nasolabial cysts
Instantonic approach to triple well potential
By using a usual instanton method we obtain the energy splitting due to
quantum tunneling through the triple well barrier. It is shown that the term
related to the midpoint of the energy splitting in propagator is quite
different from that of double well case, in that it is proportional to the
algebraic average of the frequencies of the left and central wells.Comment: Revtex, 11 pages, Included one eps figur
- …